Mindset is one piece of the puzzle but before all that, skill development/acquisition MUST come first. E.g is learning how to play tennis, doesn't matter how great of a mindset you have, if you haven't been taught the mechanics of HOW to serve (broken down into its various components), perhaps from a PROVEN coach, you are not going to hit great serves reliably well.. particularly under pressure. Sure you can blindly smash an ace every now and then but that is inconsistent luck..
Ofc at a higher level (e.g. breaking into world top 50), mindset is important for a player to hit shots in match play that he already knows how to do in training.
There is a place for mindset when learning to trade in that it's better to have growth beliefs that you can learn the necessary skills vs having a negative mindset that you can't get better with (correct) practice. However, IME trading mindset/psychology is an easy smokescreen for internet gurus to hide behind to disguise the most important fact - that they haven't got a scooby about how markets work and the actual journey to profitability
For me it goes like this:
Principles & understanding > method > behaviour (.. discipline, mindset etc)