I have been playing with the new Sony A7R with my good Canon lenses. The focus peeking on the Sony helps me get the focus exactly where I want it. And it's very, very sharp.
I think both the camera and the lens are important in getting really sharp pictures (and, of course, technique). If you are going to share on the web, then it probably doesn't matter that much.
There are companies that rent cameras and lenses. LensRental here in Memphis is one (they ship anywhere). I tend to rent the camera/lens and play with it before I buy to see if it's what I want. That might be a way for you to do. I rented the Sony A7R and was really blown away with how much sharper it was than my Canon 5DMarkIII. I don't think the two sensors are really that different; it's just that it was so much easier for my old eyes to determine whether the focus was exact. (Tho, probably the Sony is a better sensor). Autofocus can help with that but sometimes the autofocus is off.
Everything system has its drawbacks. As far as I can tell there is no perfect camera or lens. Everything is tradeoffs.
I do think good equipment, both camera and lens, can make a good photographer better, but a good photographer can take decent pictures no matter what the equipment.