Chasun isn't very good at hard at all. Never use mine.
I reruned my Ahman as part of progressing from the 60s to 90 when I was trying to get an extra L/D per month. While provoke is important on trash stages, it's almost mandatory for bosses. Sometimes the specials are just too brutal to let one happen. Occasionally you can't help it (OG procs, for example), but they may or may not be survivable (Seara may derp and not load a bomb before she AEs, that's survivable, or bomb and then not use her AE, but bomb into AE = dead).
I do have a silly Jamire team I use for trash stages (unless they're immune to something) that goes healer-less, but when the going gets tough and I can't do that, I get carried by Spectra and Ahman in particular. You do need some very specific runes for Ahman, since speed for provoke/heal consistency is important, and you'll need some accuracy so the provokes are actually landing, and his defense will become relevant (relative to his healing / turn) when he's taking a disproportionate amount of loose hits.
I wouldn't use the HP lead, either. That just gets you into trouble getting behind, you'll want Baretta's.
I wouldn't bring Chandra. He slows, but... HE'S slow. He can protect someone, but normally you're building the mons to not need it, or provoking to help stifle ganks. You could make one super fast, but you'd be wasting a Chandra building him like that.
Verad is great, obviously, whether locking trash or helping on the boss stage. Baretta (if skilled up) can solo-lock a slowed boss if he doesn't miss turbulence, but that doesn't mean I wouldn't want an AE ATB backing him up. I had an incident last reset where Baretta/Verde/Spectra were left on a boss, who was at 75% or so with trash dead, and they won. He just had to be a ninja never missing turbulence.
I don't agree with the Vero-becoming-useless, he frequently features in my wildcard slot. His stomp being on a 3 turn while being able to dot each stage's "I runed for resist" mon is handy. The whole "you'll be one shot" isn't true. He gets a lot of CC out, and since you're provoking, the fact there are resistant stun stragglers isn't a huge deal. Not saying some mons don't hit hard (when they put the dark minos high up, they hit like god damn trains), but sometimes at that point it's a matter of counter-comping and just bringing a tank. IIRC, the last time dark minos were super high up, I brought my vamp/revenge Groggo. Most mons don't hit so hard you can't handle being hit as long as you're fast and they're slowed.
My standard non-CC/dot-gimmick comp is Baretta/Ahman/Spectra/Verdehile with the 5th shifting, usually Veromos or Talc, and I'd take Basalt there in most cases if I had one unless I needed water for something. The triple fire is wonky, but my Bernard's stripped atm, and it works well enough. I do suggest bringing someone boosting your speeds, Verde/Bernard being the obvious choices. You can use other slows in Spectra's place, mine's built swift and 100% acc to land his slow as early/reliably as possible. I was experimenting with something and brought Shannon, who's currently runed a good 70 or 80 spd below my Spectra, and it was awful. Getting slow on early is amazing, even if he whiffs his RNG on ATBing.
I'm not saying you couldn't necessarily get to 70 using those mons, but I think you'd find stages you couldn't keep up with. When I wanted higher ToA H rewards, I had to break down and make/rerune several mons.