I don't thinks there much of huge difference in them, all this depends on players potentials this were difference lye . you have to start from 18yrs old to get the best bang for your buck with training. the difference from 3 to 4 is 15k a season. I don't a think 0000.3 is worth 15k$. this get higher as we go higher per~season ,per ~trainer level.
Some see that is a good things because of rapid player growth, thats ok by me, I understand the point of view. Im saying to start you don't need a level 4 trainer , It not wise to spend what you don't have. You can go basic and create a good solid player as well maybe NT level but some need to understand you don't have NT money yet, so don't go building NT players off the bat..
Then there a signing fee those trainer going to 350K$+ for level 4 and .. Level 3 is about 75-150K. I hope you can see my point of view. The best anything to start is knowing what to do , not spending what you don't know yet. Not sayng you in general ok. Im just making a point of merit.