at the fields today someone said the U2 is hotter than all the other senior bats because it is granfather into senior softball and the other bat companies cannot make a bat on par with U2 and that is why the U2 is hotter. So is this true ?

To a point, the u-2's, The Daddy, the Grey Ultra, was better yet but lasted about 6 months until it's ban.
All heck was raised about that so Miken released the ones we now enjoy, but have a counter weight in the handle at the knob. Still hits about as much and all but some others out there now are about as close as can be to the U-2. Given that, the bat is only part of the power it takes the person, ball, and other outside forces to make it come together...
Something like that anyway.