JP wiki confirms that Shou's Bishamonten's Wrath can rise over 100 count, and also notes that it raises your Attack stat, not your damage- a significant difference considering defense matters in this game. This is also true for Chen's new boost skill from the corridor.
She -is- really bulky with her synergy skills, so I suppose she has potential to be an amazing bulky attacker in a long fight. It's just that she really wants to make use of not even one, but up to -three- synergy skills for heavy stat increases (Byakuren for major passive buffs/regen, Nazrin for extra bulk, Rinnosuke for extra damage) and she's sorta underwhelming until the counter goes up, esp. without using the synergies. Her personal attacks are good, but pretty slow. Monk could be a good option for her to give her potential to keep max buffs and speed up her own slowish attacks, along with a little element variety. Swordmaster not quite as much since her personal skills are already strong, although explosive flame sword is always good if you need the element difference. Transcendent never hurts for bulky attackers, but whether it's better than monk is a pretty good question.
Potentially a good candidate for subbing the special subclasses for truly useful new attack moves, if you aim to make her a main attacker or are tackling lategame long-length bosses where Wrath will build up and up. (It doesn't go away on swapout after infinite corridor awakening.)
edit:The jp wiki seems to have filled out evaluations for everyone's infinite corridor skills. It's fun to see how much they agree with me on.

They talk about how defensive Tenshi becomes but then "...however, it has to be said that she lacks decisive things to do other than being a wall with her enhanced abilities. Most characters with high durability also boast powerful auxillary actions, so just being a wall can't let you compete with the other options." It seems that the abundance of self-buffing bosses might take care of that, though. Even if I commented on her bulky attacker potential, most attackers get notably stronger after the infinite corridor... hmm, but it's possible.
rofl, Yuuka's after concentration, always activate extra attack, currently softlocks the game. It goes into effect immediately, and you enter an infinite concentration loop without end. That's amazing.
edit again:Oh?! Maribel's corridor ability was misunderstood by me! All of the vanguard's stats are increased by a quarter of Maribel's current buffs... not, each buff maribel receives is doled out to the front row at a quarter strength. Ooh, this is notably more interesting. Plus Renko gets double effect... Renko was crazy durable as it is, with this plus a functional Sealing Club, she'll be unstoppable? As an aside note, if you max Unnatural Power and Unnatural Control, the hp loss effect is negated.
Mystia's lv6 boost from inflicting silence on an enemy will be about 30~40% stat increase, from jp testing. That's pretty significant. Combined with her other bonuses, she could finally have the stats to do real work- even be a speedy bulky attacker.
Sakuya's Private Square powers up to 4800 effect from 2800 with her new skills. Combined with steadily rising speed and mp values, this is actually a rather large amount. This could become a rather useful skill.