I have read the opposite. Generally the 7mm is going to have a better BC than the .30 caliber. There are options that can push the .30 faster than the 7mm Rem Mag, but those are going to be pretty intensive recoil.
With that said I made the switch from 7mm Rem Mag to .300 WSM a couple years ago. My main reason for switching was the short action more than anything else. My .300 WSM is 5" shorter than my 7mm Rem Mag was (22" barrel vs. 26" barrel plus the action is about an inch shorter). With my 7mm Rem Mag strapped to my backpack I ended up getting it stuck on low hanging branches way more than you would think. My .300 WSM is below my head height now so I very rarely have an issue anymore.
Plus my .300 WSM is more accurate, but that is not the norm, my 7mm Rem Mag Browning A-Bolt just wasn't a tack driver. My .300 WSM isn't either, but it is within 1 MOA and the 7mm Rem Mag wasn't.
If your 7mm is accurate and you aren't having issues with it getting hung up in low branches I would just keep it.