Technique power has always been calculated as a base plus a per-level increment, but level was pinned at zero, so that second term multiplied to nothing. Levels are per character now, and the game feeds them.

Each technique banks its own experience. Using one in combat earns experience once per battle for each distinct technique you cast, and there is a direct practice action for training one outside combat. Reaching level 100 takes roughly 4,950 battles for a median 17% gain in ability power, so the practice path is there as an alternative.

Learning a technique is priced off a real curve as well, rather than the flat placeholder it used to charge.