This debate is a storm in a kettle for the sake of arguing.

Saying that FL isn't casual is misleading specifically because that's the only existing mode for FL with no ranked mode to triage players through skill like ranked CC does (or even pve savage+), therefore expecting everybody to tryhard at the level of premades (as I've seen expressed sometimes on those forums, aka "just do your own premade bruh"), or just playing as well as skilled veterans holds no water for that same specific reason that asking your random Joe the Rouletter in your msq roulette play on a level that would be expected from a savage raider is ludicrous, or expecting casual players from the casual mode of CC suddenly be held to the same standards as crystal/omega/ultima players from the ranked mode.

Similarly, saying that nobody should try to play their best or actually optimize with organized teams in modes like FL is equally nonsensical, for the same reason that telling someone in your average expert roulette that they shouldn't optimize their job because "why bother" makes zero sense, or that they should certainly not attempt no healer speedruns of those either.

If you're speaking of modes where most audiences of players intersect, this is bound to generate friction yes, but expecting the other audiences to cater to one's vision for the mode is beyond bonkers.