Tiered structures still create new production chains to play with. A T1 assembler requires only a few steps, but the T3 requires many more steps and a lot more technology to produce. That's okay. That's perfectly fine for a game about sewing together a chain of increasingly complicated recipes. As the recipes and factory continue to grow, it's not outlandish to demand tougher and better infrastructure to go with it.unlocking another "tier" of the same thing (just a bit faster) is barely a "progress" or any meningful value for the game experience in my opinion.
I don't think it's a great idea to have higher tier assemblers and then eliminate the hard reasons for upgrading them. The early push to T2 is absolutely driven by the hard limitations of T1 being pretty useless. However at the same time players will naturally gravitate to superior T2 goodness all on their own. T2 assemblers are so all around "meat and potatoes" good that they can take the factory all the way to rocket launch. There is no explicit reason to hit T3 assemblers other than to get more because MOAR.
There are a few of ways to make tired system more clearly pronounced. The most obvious upgrade is to give better base stats. T2 builds faster than T1, and T3 builds faster than T2. It's a simple upgrade, but it's more of a soft encouragement to use better things. Another option is to create a unique upgrade that the previous tier doesn't have. For example T2 can handle all fluid recipes (barreling is dual-ingredient recipe), which is a clear new type of ability over T1. T3 has no unique advantage over T2 other than superior module capacity. That module capacity makes them so superior for beacon builds that you'd never make a serious T1 or T2 beacon factory. The bias for T3 beacon bases is so huge that you could even remove the beacon ability from T2 and T1 assemblers, yet barely change how players build factories. Just some food for thought.