General question.... What kind of rides are better?

Suppose I am able to ride 3-4 times a week. Should I do short rides? Or long rides?
I say that because I know people that do 3-4 rides a week of 1-2 hours, and they are on a very very high level of fitness (I can’t match them even when I have followed many TR plans since 4 years ago… And I always thought that mileage is one of the best options to improve your fitness…

Both. It is interplay between volume and intensity. General rule would be - do as much volume as you can and top of with intensity. It is only matters how much time do you have. You can reserve one day for longer Z2 ride (3-5h) and rest would be interval training or you can combine two, doing interval training during longer ride to train that fatigue resistance.

Can you become fast on 2h rides only? In terms of FTP, vo2 max and sprint - yes you will be fast on those springy, short races/group rides. With longer rides you will become even better and establish better basic fitness (not to mention that longer rides with intensity in them are also great from a mental perspective).

My personal experience (only second year of riding a bike) is that with 2h rides you can build high level of functional fitness but after adding those longer rides I feel more confident about using my fitness. Also those longer days helped me a lot with my interval training (better handling of lactate byproducts, better fatigue resistance, improved energy management and improved mental aspect that I can do 20 min@threshold after 2500kj without much power loss).