I was a little confused about the amount of engines we can use in digital because the Marklin control center 6021 only allows up to 80 engine addresses. Is ESU better?
The Marklin Motorola digital system was a state of the art digital system to control your trains in the 90’s. It allows simultaneous operation of up to 80 locomotives and 256 solenoid accessories all on the same layout.
Marklin together with ESU developed the MFX digital system. It works alongside the Marklin Motorola system. So you can still use "older" digital locomotives alongside newer MFX digital locomotives.
Every locomotive with a MFX decoder has its own dedicated MFX address. No other locomotive in the world has the same address. It belongs to that decoder, and cannot be changed. So you could have several of the exact same locomotive, and yet they all have their own address. Almost like having your own phone number.
In order for these decoders to work with the older system (be backwards compatible), they also have a regular digital address. The default for this is 03, and it can be changed to 01-80.
Both Marklin and ESU now use and offer MFX (ESU calls it M4). So in that respect one digital system is not better than the other.
The controller Marklin 6021 has been displaced by the Central Station controllers. They have far more capacity then the 6021 referred to in this question.