Being as there's no information (that I've seen) dealing with pet classes/souls and how scaling with the power of the player works, I thought I'd give a bit of an overview of what I've seen in other MMOs, how effective it has been, and what I think should happen in Rift.

The basic problem with pet classes and gear is this: if a nuker-type ("wizard") gets an item that boosts all their spell damage by 5%, said item equipped on a pet-class-type ("summoner"), will only increase the player's portion of the damage, not the pet's. Thus any piece of gear is not "as good" for the summoner as for the wizard. Also, because the pet's damage is not increasing with gear, as the summoner gears up, they can't get AS powerful as a wizard without "special" gear for summoners.

For those that like to skip to the end: All gear that increases the power of the player MUST increase the pet power proportionally, or pet power must be determined by the effectiveness of a SINGLE item or adornment (focus item). Any other solution will not work long-term.

My background with this is playing pet classes as far back as EQ1 (UO MAY count techincally, but being that the mechanics there 10 years ago are not comparable, I'm not including that), through WoW, Guild Wars, Vanguard, Aion, and my primary game now, EQ2. I've seen how pets can scale, can NOT scale, and their various levels of usefulness (or uselessness, as the case may be). I was a Magician (with baby necro) in EQ1, and a Necromancer from day 1 in EQ2, with the major pet classes in each of the other games covered too (WoW = Warlock & Hunter, Vanguard Necro, Aion Spiritmaster).

Now for the game comparisons:

First EQ1. From the beginning (or near enough) the Magician had their focus items. Hold onto the appropriate one for the type of pet you have, and your pet is SIGNIFICANTLY tougher. More did not equal better, but was a "have" or "have-not" situation. Eventually adornments, and other items with BETTER foci were introduced, but your pet power was dependant on a SINGLE item. This worked to a degree. Current EQ1 players can probably say the current state, but it worked. But it didn't work ENOUGH for raiders, so they (rightly) introduced the fact that your pet shared the master's resists. If a pet's innate resist (like fire for the fire pet) was higher, then it used that, but your pet's resistances couldn't be WORSE than the master's. This was due to the fact that at the time raiding (PoP-ish... I left during OoW), resistances was just about everything for most players. Pets (even with focus) were falling behind, so pets got help through sharing their master's stats. Has the idea of "single-item" focus still kept up there? I don't know. I'm guessing it would, as the "rest" of the gear that people get doesn't need to be affected by "need to think of my pet" syndrome, as once you have your "piece" you're good. But even so, for quite a while in EQ1, Necromancers were so powerful WITHOUT their pets, that they were often seen as more of a liability, and didn't even summon them. Most focus items in that game (for quite a while) only affected Magicians. Luckily, Necros there had "quite a few options" and so weren't in as bad a shape while I played.

WoW I honestly don't remember a LOT about. I haven't played since 2005, but at the time your spec (demonology in the case of warlock) determined a lot about if your pet was useful, or if it was merely a bit extra damage. Somebody else can say what (if any) solutions were found here.

I didn't play Vanguard long enough to figure out what end-game consequences existed for Necromancers and pet scaling there.

Aion I did play, and they had the same problem, but no solution. Pets for Spiritmasters couldn't fly (when it was a key part of the game), didn't scale except via the level of the player, and such. But luckily SOMEBODY there saw the problem, and even the "temporary" or "swarm" pets of Spiritmasters are now affected directly by the gear the player is wearing. The pets get tougher and more powerful as the player does. I don't think it's 100% of stats, but it's a lot of the most important ones. And pets fly as well now. Bravo to the Aion team for finding the "easiest to balance" solution where gear is equally good (or nearly so) for both mage classes there. Aion has other issues IMO (hence why I'm not playing it anymore), but they have a handle on some of the mechanics issues with pets at least.

Now EQ2. I've played it from day 1 through every expansion so I've seen what happens. In some it was fine, in others it was terrible, and it's in a "meh" zone right now. So a brief history at first to understand it. In EQ2, almost all spells/abilities have a quality level, from Apprentice to Grandmaster (6 levels of power right now), where Master is the usual top. Even pets. And for the first few years of the game, upgrading your spells was the primary way in which your character grew in power if you were a casting class. Armor and weapons had a few other effects that were useful (like mana regen), but were so few and far between that it didn't matter, and the effect of gear in general was reduced for most situations. Upgrading your pet via spell quality had ESSENTIALLY the same effect as focus items in EQ1. If you had a Master pet, your pet was end-game quality, with all of its abilities being Master-level.

Then Rise of Kunark came out. +spell damage was a stat that existed in the previous expansion, but few pieces had it, or any appreciable amount of it. Now it was everywhere. And pets suffered. And swarm (dumbfire, temporary, etc) pets suffered too. Player power rose through equipped items far more than through spell quality improvement. But pets did NOT. This was the worst time for scaling pet power, as it basically didn't. Players could get effects to become much more powerful that pets didn't benefit from. People called for shared stats, but it didn't happen. Come next expansion the wrong solution came out: gear had pet-specific stats on it, in addition to a reduced number of regular stats. So if a piece had +100 spell damage on it, then it had maybe +50 with +100 to PET ability modifier. So summoners could get gear that affected their pets, but ALL other mage gear was now WORSE as well. I'm sure their itemization developer LOVED this (I'm being sarcastic) as s/he needed to itemize for the other 4 mages, AND for summoners. This got a BIT easier with the latest expansion in that most summoner gear is COPIED from regular mage gear, plus pet stats, but not always. This is especially apparent on the "faction" or "mark" merchants. But this gear still does NOT affect swarm pets, making them useless to the point of them NOT being included in the "optimal" DPS rotation. I'll repeat that: because of bad gear scaling, they have made a whole class of spells useless.

Now for Rift. Simple answer: take Aion's solution. Make all gear that affects the summoner affect their pets. If a piece gives +20 damage to all spells, have it give +20 on the pet as well. This becomes even MORE important with the idea of swapping out souls, in that if you need "elementalist" gear as well as "regular mage" gear, people are going to shy away from the pet-specific souls, or ANY mix that has them as a part of it, as the pet won't scale, and the "summoner" gear will likely have the "less, plus pet" rather than identical stats, so your gear will be worse for your other souls than "pure" mage gear.

The only other solution that has some merit IMO is a SINGLE-slot focus item that affects pet power. Most people will give up a single slot for the purpose of more flexibility, and so that strategy can work, but the downside is the "boom, your pet is good" or "you don't have it, your pet sucks" syndrome. I'd rather have it scale with the rest of my abilities, and gain power gradually as I do.

And remember, there are pet classes for most (all?) callings in this game. This isn't only an elementalist problem.