why wouldn't you use a mid-priced prosumer camera like the 5d mark iv primarily for web? there's professional photography done for web only, and you're right - something like an 1d or a phase one back on a medium format camera would probably be overkill.
If you're shooting ONLY for the web, which is mainly what I was referring to...then a DSLR like the 5Dx is overkill.
Now, I do realize that most any great image taken, for print, etc...will *also* likely end up on the web too, no problem.....always nice in the pro area to shoot for print and down-res as needed. But I took the "shoot FOR web" to be someone only shooting for their private website, etc....and in general, these DSLRs would be overkill for them.
And if you consider close to $4K a pop for body ONLY...to be mid priced...whew, you have more disposable income than I do.