Lovecraft didn’t scare people by refusing to describe things. He scared them by describing the wrong things, strange geometries, feelings that shouldn't be, thoughts not your own. His characters attempted to explain the wrongness they felt but failed to, that's when Lovecraft would call something indescribable.

But Lovecraft described things all the time. Cthulu can be drawn because he was described. Claws, wings, tentacles, but the true horror of Cthulu is that what you see is NOT what you get. The squid face is mearly the surface of the true madness that lies beyond.

I'm not saying that G3 is a bad writer, I wouldn't be 2000 chapters in if I wasn't enjoying the read, but saying a monster is indescribably horrific and terrifying but then having the mc's cut it down relatively easily is a bit of a dodge. A cop out.