Not only in multiclassing, but some great features of some classes are also lost because they are over level 10. With only a level cap of one level more, 11 you can have the warlocks´ mystic arcanum, artificer´s spell-storing item, fighter´s third extra attack, rangers´ and monks archetype feature and rogue´s reliable talent... and I supposse we will never get to see any level 6th caster spell unless it´s in a scroll.
Also, certain feats require you to be at a certain level? Where's that in the rules, I don't see it.
Oh, no, it´s a homebrew I made, if that´s what you are asking because I allow a free feat at level 1 and if I do not create a list of feats with level limits all the players will take war caster, arcane secrets, sentinel or lucky at level one =P and those are not meant for low-level parties, usually; and to encourage´em to try feats that people often don´t use and can be fun for your character.
