I've used industrial vitamix blenders at work and I have a Ninja at home. Unless you're making smoothies every single day there's absolutely no reason to pay 400 bucks for a vitamix. A ninja will suit the average person who needs a blender / food processor almost every time.
Tl;Dr: If you're cool with buying a Lexus to drive 5 miles to work every day instead of a Toyota then get a vitamix.
The quality of your blending experience can determine how frequently you are motivated to blend things. I'm currently living at a place where the only blender is a Ninja, and I never want to blend anything, because I just don't want to deal with that hassle. When I had my Vitamix - the lowest-end $250 refurbished model - I did make smoothies at least twice a week.
That's not to speak of the fact that some things, like making nut butters, are simply infeasible on a lower quality blender.
Plus I just looked at the price. I also have a Ninja - $90. Vitamix - $600. I'd have to be blending a whole lot to shell out that much, but I'm not, so I didn't. The Ninja works great and is the best blender I've used so far, so I don't see a reason to upgrade. Use what works for you!
The Vitamix is the standard choice for restaurants. It's consistently out performed every other blender on the market for literal decades, is built like a tank, and makes smoother purees than anything else.
It's an absolutely insane purchase for a home cook to make though lmao. The ninja you have, while it might not be as well built, works like 90% as well as a Vitamix but for a tiny fraction of the cost. And for a home cook that maybe uses a blender once a day, it doesn't make sense to pay for the durability and slightly increased performance of a Vitamix. Whereas for a restaurant that might use a blender dozens of times a day, it's absolutely worth it for them to go with the Vitamix.
Alternatively: get a used Vitamix on eBay or elsewhere. We did that last year and saved 50% on the cost vs new (I want to say it was $200 vs over $400 new). From what I’ve read a Vitamix like the 5200 is pretty easy to get parts for if something breaks on it.