Some of the Axiom[/url] racks are worth a look if you are putting a rack on a non-touring bike. Not just in terms of getting a connection to the frame without braze-ons.
A mountain bike frame will generally have quite short chain stays so if you are a bigger rider, or more specifically have big feet then you’ll tend to get your heals catching the pannier.
The streamliner and unfit racks have a sort bracket that cranks backwards from the dropout, so it clears disks calipers but it also moves the rack backwards a bit too. At the top it connects the seatstay bridge rather than the stays themselves. The plate at the dropouts is steel and easy to bend/cut/file if theres any fouling around the drop out or disk mount. If you don’t have the little threaded rack / mudguard hole on the dropout you could probably put your qr through the plate instead.
I use the streamliner road as I tend to only use the one lightly loaded pannier so having it sit a little more inboard helps.