I played through on deathmarch without upgrading Quen at all, focused almost solely on the combat tree. It was difficult, but I honestly don't think it was much harder than if I had invested in Quen (I went through with a sign focused build the first time). There is a lot more variety in play styles available than people give credit to in this game. People just need to learn to branch out and not lean on early crutches so much.
When something simple works throughout the entire game, it's not an early game crutch, it's just first order optimal.
[disclaimer, I haven't finished the game yet, but from everything I've heard from people I've talked to or just googling about Quen, what I've experienced seems to hold true throughout the rest of the game]
The obvious difference is that Witcher 3 isn't a competitive multiplayer game, so these things aren't quite as immediately apparent.
edit:
Let me be clear that I think this is actually totally fine design philosophy. I really like its use in Dark Souls, where you can't choose the difficulty via in-game menu, but instead you choose whether you'll use a shield, high poise armor, pyromancy, etc. which all make the game easier without breaking immersion.
I'm only commenting on the idea of an "early crutch".
