Splash with scorch shot is 6.88 feet, splash with stock rocket is 9.1
While that does seem like a big difference, it's still large enough (combined with its good firing speed) where it's difficult not to at least scrap your opponent.
If you miss there is no burn or detonation
the chance of missing is pretty low
A strat that is much better if you use the flare gun
potentially, yes. a good pyro can be much more efficient with a flare gun. however that requires a lot of practice with weapon switching reflexes and predictions (as i have said, the flare gun is much more dodge-able and you must land a direct hit)
While I don't think the scorch shot is necessarily op, it is very irritating to deal with and that's why i think some things should be reworked and/or nerfed
how 2 get better at lobbing the bombs
im bad at demoman
by bombs do you mean pipes? if so, a good tip is to not spam them until your clip runs out (which too many demos do) which will make you be stuck with one of the slowest reload times ever. Also, something that takes practice is predicting your opponents. Maybe shoot one pipe at them, see how they react, try to see a pattern in their movement, then give it your best guess and fire.