I think the Training action is way too potent as it is. PbtA doesn't have that kind of granularity.
Viewing post in Sparking! A DBZ-Inspired PbtA Game comments
In other pbta systems, gaining +1 to a single attribute is 5 Experiences. +3 in a stat is generally considered the reasonable maximum one can go. You can also buy Moves and other benefits this way.
What you've done instead make experience into a single roll with massive benefits for success. This is a nightmare scenario.
What I might suggest instead is that training applies to specific threats or goals. PbtA is a narrative system - training should either be background justification to spending Experience or, if it's a Move, it should have a direct narrative purpose.