You merely cut off the actual 7th-9th level spells, but you keep the slots. It actually gives more incentive for those classes to pick up and apply metamagic feats. (It certainly makes Heighten Spell more attractive.)
I think there was also a feat or something that allowed you to divvy up what a spell slot actually obtained; for example, you could have a 2nd level spell slot instead work as 2 1st level spell slots. That would be another great option for such a game.
This would be the easiest and minimal change to get your desired result Nerdtothe3rd. It's not the classes or spell slots but the spells themselves that people are finding problematic.
Additionally, if you find you want one of the cut spells back, you can allow it as a ritual with a long (10 minute or more) casting time and a minimum caster level requirement equal to the level that class would normally get access to the spell.