If you want to make it so everyone can que and everyone isn't up against totally unbalanced teams just do the following.

Make 3 queing tiers that anyone of any rank can que for.

T1= Caps at 200 Valor
T2= Caps at 500 Valor
T3= Uncapped

Make it so that even if a P8 ques for T1 their valor is 200 no more regardless of the amount of valor gear they have equipped. Yeah this might mean queing for a T3 warfront might be really long but you have other options you can do in this case and if you don't like it go put your P8 group together and farm PvP rifts instead.

2ndly MAKE IT SO THAT TEAMS CAN NEVER HAVE MORE PLAYERS THAN THE OTHER SIDE. Simply make it so that the yellow bars that prevent people from leaving remain. If One side has 6 the other side has 8 then bam only 6 people are allowed to leave the side with 8 players. When someone dies then the bars would let out another person.

Balance omg how easy was that!