Conclusion from dpreview:
The EOS 90D is a DSLR that functions most reliably when used in live view, thanks to its excellent Dual Pixel AF system. Through-the-finder AF is less reliable, by comparison. The camera also offers excellent Raw image quality and usable full-width 4K in a well-built, weather-sealed package with fabulous ergonomics.
It’s a sensible upgrade if you’re curious about the benefits of a mirrorless camera, but aren’t ready to commit to the form factor.