froslass is a completely different story. i've tried and tried, and i still don't see a niche for this thing in the ou tier. without snow cloak legal anymore, its only viable set is a lead sasher that essentially spikes up, attempts to catch something with destiny bond, and then dies. one of the major flaws of this set is that it's completely beaten by any variant of tyranitar. ttar uses crunch as froslass gets a layer of spikes and is brought down to its sash, then sand finishes it off. froslass can't even use destiny bond, because when weather kills you, destiny bond won't activate even if the pokemon bonded to is the weather inducer in question. it also has literally no offensive presence, with a measly base special attack of 80 and a movepool consisting of ice beam, shadow ball, thunderbolt, and not much else. and with defenses of 70 / 70 / 70, plus a weakness to steel, it can't even act as a decent spinblocker. there is no place for froslass in ou.
It tends to either get two layers down reliably or one layer and a major KO (like Scizor). I've had great success with it, and it's unexpectedness (most expect Taunt, Detiny Bond, and an uninvested attacking move) has sometimes allowed it to deal damage to large parts of an opponents team (an example that has happened to me. Opponent leads with Scizor, is fried by HP Fire. They figure that HP Fire was my one attacking move, send in Dragonite to set up. Dragonite eats an Ice Beam and is in KO range now, they send in something else, which I can hit with Shadow Ball. That goes down, and I get a layer of Spikes.) It also beats all spinners/Magic Bouncers/Deo-D one-on-one, other than Tentacruel. And, as I mentioned before, Scald is only a 3HKO without investment, meaning you get 3 layers down. 80 base SpA isn't that bad either, especially when you consider how useful its STABs are in the current metagame. Also, its speed means that with Focus Sash it only needs to 2HKO a threat to eliminate it. Froslass is also bulkier than you give it credit for. An uninvested Landorus-T (and this is only for the sake of example) using Stone Edge on an uninvested froslass has only a 68.75% chance to OHKO. Tyranitar still sucks though, but you can always not lead with Froslass and hold it in reserve as a semi-offensive Pokemon/emergency Spiker. I personally would actually be willing to push Froslass for B rank as it is very useful, but not good enough for a higher rank.