So I ran into something online as a rando companion yesterday that I want to share, particularly because the case where I saw it used sounds like an infamous one in places including this thread.
One of my companions was a Skill Swap Polteageist with Weak Armor against Tera Ground Kingambit. Given how raids work, Speed and turn order seems really screwy to the point I just always assume the opponent will act before me (especially when the go-to attackers for randos are slow BD users already like Iron Hands and Azumarill). The trade-off usually works to our benefit since the speed doesn't change the number of actions to my knowledge, just the order every "set," so debuffing DEF just for hitting the boss as usual, and more importantly removing their own ability if it's a problem one like Defiant to allow debuffing (whether deliberate or avoiding punishment on procs like Play Rough or Liquidation). Being able to debuff these guys obviously seems helpful given they hit like trucks with usually-neutral coverage for non-STAB Tera types, and it's a way to increase damage without breaking pace in case they dispel Stat changes on either side.
The most interesting thing I noticed is that it doesn't seem to revert the boss's ability when they clear Negative conditions, even if they clear the DEF drops themselves. This seems like a really useful support effect in particular since, if you can deal with the Speed Ups, it provides action-efficient damage boosts.
Also makes me wonder about the value of other "exploitable" Ability Skill Swaps, or even just removing the boss's ability via methods like this in general since some of the hardest ones are in significant part because of them. I saw Skill Swap mentioned back on like Page 2 with an Umbreon, but there appears to have not been too much buzz about it since then, and this example came to mind since the ability could Sandbag the boss beyond just removing their innate ability.