Originally, each faction was to have a bound archetype soul. Guardians had Paladin, Assassin, etc. and Defiant had Reaver, Nightblade, etc. This original idea was scrapped. Now, we can have any soul at character creation and we get our second and third ones very quickly thereafter. This has created problems with those archetype souls. Particularly in the case of the Cleric with Sentinel and Purifer.

These instant heal souls are nearly identical. So much so that they use the same icons albeit for different effects (quite a pain remembering which yellow cross does what). The roots have the same sort of abilities at nearly identical levels through level 16. The branches on the other hand are where the additive bonuses between these two souls are found. This is the reason to have both souls for a healer. Also, the Sentinel has the raid-wide heals that the Purifier does not.

These souls were designed to be starter souls. They have both healing and damaging abilities. In practice though they are not the best starter souls especially since all souls are available at the start. In fact these two souls are best added to other more offensive souls for PvE. In groups, where they are used most intensively, the inclusion of damaging abilities is superfluous. For a dedicated healer, it is impossible to fill in the branches of the soul trees without putting points into non-healing skills.

All these facts IMO call out for a remix of these souls. One should combine all the heals and the other can have the defensive (and damaging) skills. This would give much more variety to soul selection and potentially create a great buffing soul for the Cleric class.