Honestly the simple answer to this is to include everything. The game is called Halo Infinite, so go big with it. Sure, weapon balancing in the sandbox will be a pain in the hide to do, but it would still beneifit the entire playerbase by giving them such a large and strong selection from every armory from every game. If anything, restrictions would and should be placed in competitive playlists (because they hate fun) in order to keep it fair and to keep Comp balancing small.
Just put in everything.
EVERYTHING.