Davey not to muddy the water too much, but to many people Paris is almost like a drug. They love it and can't get enough of it. personally I feel Paris' strong force when I go there, to an extent understand it and certainly enjoy it. But honestly I'm ready to leave after a couple/few days. It's an amazing city, but it's still a big city, and I'm just not that into it.
And there are still other who dislike Paris and actively work to stay away from it. The Frenchman who married my neighbor's nanny for instance live in Paris because of work, yet he thoroughly hates Paris, can't wait to get away from it.
You are going to hear a lot of "Paris is a drug" people tell you that a week in France's most intoxicating locale is barely sufficient to even get started there. That's true for them, and I can sympathize with their perspectives. But certainly not true for me, and maybe not true for you. We are all different, so know yourself. If you're the type who'd thrive off a full week in NYC you'd probably feel the same about Paris.
The train to Strasbourg from Paris is safe at any time of day, as is the train from Strasbourg to Colmar. The Paris train station you'd like depart from is also safe, although it is a big city train station with the usual cast of scumbags looking to grab a purse or con you out of your wallet. But you'll keep you head up and be fine.
I'll also push back on the notion that Alsace isn't unique. I most certainly is, both in architecture and culture. If you want to see it, it's well worth your time. Last summer I went back for the fourth time in my last six trips, albeit a couple of those were stops of convenience passing through as opposed to a select destination.
You say 2.5 hours on the train from Zurich like it's a tough assignment. The train though is so easy and generally relaxing and pleasant. Look out the window and see new and interesting landscapes, catch up culling your photos, eat a yummy sandwich or pastry from the train station. In the US I do tend to think of transit hour as mild forms of torture, but in Europe I actually look forward sitting on the train, exhaling fully, and taking it easy for a bit.
So if it was me, and of course I'm not you, I'd fly to Zurich, train to Colmar, and post up in a nice AirBnB for 3 night. Day trip to Strasbourg and visit on of the pretty villages too. Then 4 or maybe 5 nights in Paris.
I do think that Paris at the end of a trip is nice. It's the major leagues of Euro travel and I like to do it when I need my energy lifted and when I know I'm out soon so willing to go all in.