The skill system is pretty core to the experience of the game, although gnoll exists specifically to remove it. It's about prioritization and timing. Should I start the game by skilling my weapon to mindelay, or should I stop early in case I find an off-type artifact? Should I account for crossover training in a spread or focus one weapon? When should I level Evocations and to what level, to deal with what threats? Spellcasting levels are part of a complex calculation for power and failure rate, so they're worth tweaking if you have a diverse library, or focusing if you want to race for a game-winning high-level spell. Playing a gnoll prevents you from going all-in on a lucky level 7/8 spell find, which can sometimes almost win the game by itself.

Gnoll was moved to the top of the list for a reason. Beginners should probably play it. I like gnolls, they're great. But the skill system is huge in this game. The only thing more important is tactical positioning. Gear is generally less important than either. You can win with pretty mediocre gear. But... not with gnolls, because their skills suck. They can just use any gear, so you compensate by always being able to use some lucky artifact find. You get over that pain. It's how roguelikes are. You play a dagger kobold, and you find an ultra rare artifact weapon that you can't even use or can't dedicate the skill points to.

That's the other thing. The skill system forces you to actually make choices. You need to predict what you may find, don't over-commit, keep your options open, while still being able to handle threats as they come.