The difference in BB height between a tourer at 275mm and a mtb at 295mm won't be felt much in handling of the bike in a loaded touring scenario. Unlike road or mountain bikes, touring bikes generally lumber along without much leaning into curves or sudden directional change.

BB height does determine how easy it is to hold the bike with one leg down at a stop, which is critical when the bike happens to be loaded with gear. For a given saddle height, the higher the BB, the higher the saddle, and the further your leg/foot has to reach to plant on the ground. A high BB means you may get only a toe onto the ground, especially if it's an uneven surface. This may necessitate leaving the saddle at every stop, both feet grounded to keep the bike standing.

Touring frames have a very low BB height, partly for a lower center of gravity to improve load control, partly so you can get a foot down at stops easier, and partly because there's no reason for it to be any higher. Road frames have a higher BB than touring frames to give them more pedal clearance when the bike is leaned into curves. MTB frames have the highest BB, to avoid pedal strike on rocky singletrack.