The movement debuff is a pretty minor inconvenience that suits the power concept of just...moving stealthily (though in fairness the character with it I've played the most is SR and has Quickness to offset it). Why not remove Stealth's suppression of half its Defense bonus in combat instead? I imagine there's a concern about having too much Defense available but builds are still limited to 4 pools, one of which almost always goes to Speed for Hasten anyway. Having one more option for a small but consistent chunk of Def alongside CJ, Hover, Weave, or Maneuvers would increase build flexibility, give people more room to build for concept while chasing mechanical performance.
Though, wording question about the Invisibility change: does 'most of your Defense will suppress' mean it'll suppress your overall Defense when you attack with Invisibility on, or just most of the Defense granted by Invisibility itself? If it's just the latter and some of it remains in effect on top of whatever else you have, then that could make Concealment a viable contender for build space anyway, albeit at the cost of an extra power pick, especially if the unsuppressed value falls between CJ's (1 power pick) and Weave's (3 picks).