YouTube 4K is barely better than decent 1080p.. here's a thread talking about this very topic:
In terms of why your 200D 1080p is soft, that's a Canon DSLR, and nothing to do with 1080p.
My advice is this:
Watch a bunch of videos ON VIMEO to see what cameras are really capable of in 1080p - you'll be amazed. If you decide you want/need 4K then so be it, but do yourself a favour and try and actually look at images instead of brand names. And yes, "4K" is a brand name - just how the manufacturers of TVs marketed it to people to get them to replace their perfectly good 1080p TVs. Most movie theatres have 2K projectors, so lots of marketing was needed to get people to buy a TV that has 4 times as many pixels as a movie theatre.
Forget about Canon, or be willing to pay the Canon Hype Tax. The internet is full of people who think that Canon is the king and everything else is second class. These people are fools who don't know how to tell if a camera is any good or not so they just check what brand it is and then go hang with the people they know will make them feel better.
Canon has great colour science - so do most other brands. Canon has great AF - so do many other brands. Canon cripples their products because the fanboys and girls will buy whatever they're selling anyway.
Go to the ARRI website, the RED website, and the BM website, download their sample clips and have a look at how plain they are. Try and colour grade them and see what you get. This should show you that the glorious images that you are seeing online from the cameras that you're lusting after, the Canon ones especially, are due to the skill of the operator in post, rather than the manufacturer who designed the camera.
Good luck. My journey started with me wondering why my 700D 1080p files looked so bad and thinking I needed Canon colour science and 4K to get good images. I've now deprogrammed myself and use neither Canon equipment nor 4K, but I've spent a lot of money on glass.
Good luck.
