That's not true..Vmc is predicated on standard conditions...such as full power, 5% deflection...
Find me different Vmc numbers at different altitudes, weights and temps on a light aircraft, differing power ranges......you won't.
Not only is it possible to fly below Vmc and the plane doesn't roll over, but I have done it.
Keeping the Vmc roll from happening is a very easy thing to do, pull back enough power to keep the plane level...now with the power that you do have...what is it doing? Climbing, descending...??
Imagine being a plane that is very light, in Alaska, 20 below, power needed to keep that plane up will be much less on one engine...that reduced power setting on the good engine might be enough to keep it up in the air.
120 degrees in Africa?...sure, I wouldn't try it....No one in there right mind will intentionaly try to fly below Vmc, but the ops, or situaton might require it..better be ready for it, then just crash like everyone else.
And let's face it, when it comes to safety, don't throw stones..if your running flex at an airline, planning balanced field into the stopway with 200 people in the back, looking over at your 600 hr FO, it's a hard sell to preach safety...
With the advent of VGs, putting Vmc typicaly below stall, this issue is almost moot these days on something cabin class like a Cessna twins...