Well, looks like I'll be switching back to 2.6 for the foreseeable future, which makes me sad. I ran into this problem (namely, the pressure on my tablet doesn't register correctly) while doing my latest handdrawn style test and it looks like there's no fix on the horizon per the 2.7.5 release notes page:

GIMP 2.8 relies on a newer version of GTK+2 that unfortunately has partially broken support for graphics tablets such as Wacom. If your graphic tablet doesn't work in GIMP 2.8 as it should, we recommend downgrading to 2.6 until we release GIMP 3.0 that relies on GTK+3 which has fully functional support for advanced input devices.