Lance just seemed really weak to me in general, pretty much zero strats and trying to brute force. Couple that with him losing his championship status, being an elite 4 member in start of JN and than being the new champion Johto and Kanto kinda screams to me he isn't that strong.
1) Lance was 2nd in the PWC last season. There's no reason to assume that all the other Regional Champions were not in the Master Class before. If anything, it would be a stretch to assume all the Regional Champions joined the same time Ash did.
2) We don't even know whether he "Lost his championship status". This is just an assumption. If anything, there's far more reasonable to assume that he probably stepped down due to his G-Men activities or some other reasons and reclaimed the position (Because, if there was a Champion who was relative to Lance in Strength, why isn't he or she is in the PWC Master Class)?
3) Lance's strategy was not exactly "Brute Force". He was more adamant on relying on "Dragonite's" Tankiness and offensive prowess. This is something that we've even seen Ash use at times. This literally helps Lance against a 4X type advantaged Pokemon Initially and would've probably even helped against Mega Gardevoir if Diantha hadn't made the prediction in the end as Lance lowers Gardevoir's speed with the initial Max strike and would've Hit Diantha with a Point Blank Hyper Beam (If she hadn't dodged and directly powered up her Moon blast).
Honestly the fact she's still top 4 seems like a pretty straight answer by the narrative to me. She'll obviously be destroyed by Leon, but I still believe she deserves to be put above Iris, Alain and Lance.
Isn't this you literally contradicting your own point lol?
You initially called Lance weak and in the low tier among the Regional Champions, then why would a win against him put her on a tier against Arguably tougher champions?
As for your earlier point about Leon and Cynthia, I think I'll honestly bump Cynthia up to the Leon and Ash tier
There's literally no objective reason to do this.
As to why Ash is at the top? Come on man, he's gonna win the whole thing and be the strongest monarch. He deserves to be there
Again not necessarily. We don't know whether Ash is going to win or even push Leon. We can only conclude this after watching the two actually batter. However, I guess it is reasonable to assume Ash at the very least will likely be Leon's tough challenger.
So the final tier list would be:
Tier S: Leon, Ash
Tier A: Cynthia, Steven
Tier B: Lance
Tier C: Iris, Alain
If Diantha pushes Leon to go all out, she'd jump to Tier S. If she performs relatively well, she'd be tier A. If she's crushed, she'd likely be in Team B.
Diantha would have to do worse than Alain against Leon to fall to Tier C and this would also automatically bring Lance to the same tier.