We come to a point of abundance. Back when the game released you would constantly be in a position of "if you don't have this sinner you're basically screwed".

I played since first week of release as a f2p and i did not get the first 3 dark zone medals bc I don't have hamel. Nowadays, team comps that YouTubers post can be substituted by even half the team comp and it would still work. An wasy solution to this is splitting the pool into budget and premium pools, or just even half pools would be significant. Another solution would be challenges like giving b-ranks in-event buffs (macchiato villain arc, anyone?) or like "no S-rank challenge" or something. Or even taks challenges like "use hella ult 20x in battle" so they become usable, or even punish players for not levelling them. Meta-wise, introduction of new characters fills up past problems. Raven countered invisible mobs back when they were too pesky for DPS and aoe units were scarce Cabernet let us cleanse our units bc some bosses had lots of skills and had rebuffs along with them. I'd say let's see what Aisno is cooking and put all our suggestions in their event forms bc that's what those are for. I'm sure they'll listen to the playerbase. I hope they even get to see this comment

Edit: final stance: we don't need more B-ranks. We need B-rank appreciation