My 90D isn't "just" for scanning either-- I've been considering the upgrade. I honestly really like the optical viewfinder on the 90D, and I'm not happy with what appears to be a cash grab by Canon on RF lenses (very nice, but everything is an "L" series, and priced accordingly). Bit outside the scope of this thread, though.
Not to veer too far off course, if it helps any, I use an R5 as my current dedicated scanner, shoot a pile of on location and event stuff with a pair of R6s, use an RP as my personal main daily carry, and use a 90D as a dedicated tethered studio camera for headshots, product photography, portraits, etc. I couldn't be happier with the R series of cameras, and I've also been considering the R7 to replace the 90D, though what I'd really like to see is Canon release a high megapixel (like at least 80MP) R camera, get that, then cycle the R5 in to replace the 90D. assuming I haven't worn the shutter on it out by then. It still might be worth sending in for repair, but it'll have a fairly high shutter count by then.
In terms of lenses, not all of the RF lenses are L glass. I have the 24-105L and the 70-200 2.8L (for event work, both basically live on the R6s), but I also have the RF 35mm STM, the RF 50mm STM, the RF 16mm STM, and am planning to get the RF 24mm STM in the not too distant future, and I'm pretty happy with those lenses and they're not *that* expensive. I also have the EF-s 10-18, the 40 pancake, and the EF 50STM, those last three go with the 90D, and how I use them, they're all totally passable in the image quality department. Zero complaints. All their EF and EF-s glass is also totally adaptable and works perfectly, so you can still use your current glass and update to RF mount as funds permit for your most used focal lengths.
For me, personally, where the RF mount really shines is you can adapt other mounts to it. My little RP has the Voigtlander 40mm Nocton 1.2 in M mount mounted to it and it is *awesome*. Just turn on focus peaking in the menus and you can see what is in focus and what isn't as you rack through focus in real time, then punch in either 5x or 10x for critical focus through either the viewfinder or the back display, then take the photo. Total and complete photo taking bliss. Turn on exposure simulation and you see what the image is actually going to look like through the viewfinder with your chosen picture style before you take the photo and can adjust composition, exposure, aperture for dof (on the voigtlander, Canon's own lenses always go wide open to autofocus). It's never been so good. If you get crap photos with that, it ain't the equipment, it's the user.
We haven't even gotten to my film bodies, and I have a number of those.
