If you are going to compare a HT with fixed rubber Duckie antenna to a mobile higher powered rig with an external antenna; there is just no comparison, whether or not either or both are on VHF or UHF.
The mobile is always better in that situation. Irrespective of the difference between 2 to 50 watts, the fixed HT antenna to mobile external antenna, is going to be a big differential.
I am not aware of Amateurs who use 1,500 watts for VHF/UHF unless perhaps some sort of experimental transmissions to a NASA interstellar vehicle.
The major advantage of 2 watt FRS radios are that they are easily purchased on the way to a field trip by a road group and GMRS users can communicate with them.
For the most part GMRS users cannot communicate with MURS that easily.