Oceanhorn 2 is an open-world action adventure taking heavy inspiration from Legend of Zelda. It's predecessor was about the length of the recent (new) hand-held Zelda games (~15–20 hours), the sequel is claimed to be longer and bigger.
Overland is a turn-based survival game. I have seen it described as something like a hybrid between Oregon Trail and XCOM.
Beyond A Steel Sky is a story-driven cyberpunk adventure game.
Atone is a narrative 2D puzzle adventure/RPG game.
The Bradwell Conspiracy is a first-person narrative exploration/puzzle game.
Does
any of these games sound like a simplified, one-button casual game to you?
I'm not saying anything coming to Apple Arcade will offer a deep gameplay experience. Quite contrary, there are quite a few games in the announced line-up which seem to be trite shovelware crap. But claiming there are nothing but simple casual games coming is either uninformed or actively ignorant.
There certainly won't be any "triple-AAAYYY" games like GTA V, Assassin's Creed, or Battlefield coming to Apple Arcade, as these simply would be out of the scope of the targeted platforms – both performancewise and playabilitywise –, but good, acclaimed indie games in the vein of LIMBO, Hyperlight Drifter, Tacoma, FTL, or Into The Breach are absolutely a possibility.
All depending on Apple's perseverance, of course. If they lose interest in gaming again a few months later (as they were prone to do in the past), it's all for naught.