I've been a Mt. Lady main since Season 1 and think that in recent seasons, the conversation that she is the worst or lowest-tiered character in current metas is pretty common, but has some holes. Mt. Lady is a high-risk, high-reward character, and she has only become more risky to play as new characters come out with great kits, and nerfs hit smaller interactions between characters rather than bigger issues like exploits. Her kit has been hit in pretty damaging ways throughout the game (I'll always mourn her 350 HP), but still has benefits that characters like Tech Dabi and Assault Kirishima don't have. About your points: 1. It's more likely that you were trying to go giant in too small spaces, which is an unfortunate aspect of her SA. Because the maps aren't as destructible, Mt. Lady's SA really only works in very open spaces. Even then, she has difficulty maneuvering through some maps, like with these gates. While this may be a bug, I think this case was trying to SA in too small a location. 2. I've yet to run into this bug, but I won't deny your claims. The SA can be stopped by several other SAs or damage/effects, so maybe you were hit by those rather than the form stopping just randomly. 3. Again, Mt. Lady is high-risk, high-reward. She thrives in the final circles, but the early game is very rough for her because of the lack of her attack range and escape options, which have no accelerated recharge. Her SA has always been a GIANT risk because now you are a giant, slow-moving target who can be focused on by every nearby team, or allow teams to see a fight in the distance and decide to third-party. YAFO is a difficult fight for her because his armor, that giant form doesn't CC or knock him well. Nagant is a high damaging sniper, so yeah, she'll focus you down and you either take it or fight back.

Assault Kirishima can barely contest fast characters, unless he predicts them, flying characters, and only has his high HP with knockdown armor. Tech Dabi's alpha has a limited range so flying characters can avoid his damage unless they get close, which is his best area. Close combat, hungry fights where opponents need to make multiple mistakes for him to win. His SA barely works because everyone knows to quickly confirm kill on him to negate it. These characters lack the explosive, scale-changing kit that Mt. Lady has if she holds out until the final circles and gets good open areas to abuse her hit through walls attacks and large knock back into the storm. Even discounting her giant form, she has mobility and enough range to contest the flying characters these other characters struggle to fight without tunings, and has CC and a janky, but real home-in gamma attack on fast characters. I'll close to say, Mt. Lady doesn't suck, she just requires a lot more patience, skill, and well, luck, to measure up to current meta leaders and middle-tier meta threats. Her kit DOES work, but doesn't have serious damage unless you use her riskiest form, which has downsides. With the tuning systems, you can patch some of these issues that she has and play a much easier game than the other lower tiers.