The problem with reclassing in FE11/FE12 was that there were basically no limitations. Like, you could reclass every unit, every chapter, with no penalty. At least the new way forces you to make decisions about who you want to use, what class you want, etc. The old system required no foresight: you could have most/all your units mounted in a large-map chapter, and then immediately switch everyone to magic users for the next.
And I'm confused what you're saying about this game forcing you to pick from classes with "low/no weapon rank" - but how is that not true in FE11/FE12? If you reclass Nabarl to Cavalier, his lance rank is going to be the class minimum.
The new system gives a reason to actually objectively look at different units and compare them. Like "Sumiacan promote laterally to X, Y and Z, whereas Tiamo can access A, B and C" rather than every "who is better" debate just boiling down to stats and availability. If you ask me, some limitations make the game WAY more interesting - because it forces you to utilize strategy which is what attracts most people to Fire Emblem.