You asked, "Am I wasting a big container on plants will little root system?"

Yes. Sort of. :)
Ideally, you should use a pot no more than 2-3 inches bigger than the root ball of a plant.

I can't say I always follow this, myself. I have a few agaves that are a good 6-8 inches in diameter. The pots that they are growing in are supporting the actual plant (the leaves are resting on the rim) while the root systems are small and no where near filling up the pots.

Hello,

Succulents come in lots of different shapes & sizes. If you might suggest what type(s) you mean, or perhaps share some pix, we might be able to answer that question.

As mentioned with out knowing what specific type of succulent plant(s) you are referring to suggesting a pot size is difficult.

Fast response:Most root systems only need wiggle room While others could use more than wiggle room ( extra space) for reasons such as root flairing and caudex forming.
Small pot example would be any type of Adromischus marianiae as they all have slow growing roots and are also slow growing.

An estimate for any of these types of Adros would be able to grow for at least 5 years ( very possible even more than five) in a pot that's one inch deep and 2 inches round.

How much soil the small pot uses is relative to the pot size.

Both pot and soil would need to allow root and plant growth while supporting the plant to remain stable inside the pot. If to hang or drop off the edge or sweep then the pot has to also support the dropped weight wile avoiding possible top heavy pots with plants already in them .

What can be referred to as staging, sometimes you can soil fill a "small pot" a few times before the plant finally gets in.

It's also possible to fiiler or to down size an already to big in size pot. If interested I can post some guide pics to demo a pre filled oversized pot by deconstructing to reconstructing.