On product this class really shouldn't be a problem.There is so many ways and opportunities to work around an enemy pyro on product I honestly can't believe this is used as an example to spark a discussion about the class again.
I do agree that the pyro is slightly overpowered though. I could go into detail why the class is broken on 5CP, however it is enough to point out that the only thing making this class unbalanced in 6s is the heal beam. Look at Olghas heal stats. This class wouldn't work in the way he plays it, if it wasn't for the beam constantly on him.
Now, if you really want to fix this problem without valve because of one dude playing this class permanently, you either adapt to it by actually trying to abuse the disadvantages of having a beam pyro or you enforce the usage of the backscratcher so a tanky, waddling space-maker can't happen in the first place.