OP wants to play a specific class in the savage raid.
You get faster LB fill up if you have unique classes.
On day one many PF groups limit their group to one player per class and can set that in PF to enforce it.
OP is finding groups that already have their desired class in the party and is therefore unable to join and seems unwilling to make their own.
To the OP:
PF rules are defined by the player and not SE. You join in via PF, you play by the rules set by the starter of the PF group. Don't like their rules? Don't play with them. Start your own or join one that you like the rules of.