D&D 1E Replacement for weapon specialization?

[Musing Mage]

For example, why make a PC specialize at first level. Why not wait till later?

This is pretty much the one thing I do - rather than allow specialization at 1st level it doesn't become an option until 4th level, and even then you must find a mentor who can teach you. Bow specialists must spread it out over to two proficiency acquisition slots, so basically 7th level is the earliest you can get it, but I keep it btb, which is quite devastating but worth the wait.