For one pyro 3 is already a good pve boss killer, you can probably burn through bosses in 15 seconds for one cycle of skill casting, 30 seconds for two.
The problem is thauma. its like taking a support class for dps means. and pyro and thauma are like pve and pvp classes that dont go well together.
second, what stat are you going to build? if u focus int, when you use transpose you will have something like 20k health cap but your actual health would be much lower than that. so after you transpose you would have to use a lot of hp pots to get to max hp cap. if you focus con, then at end game it wont scale as much as int and you will probably have half as many stat points than int.
for pvp, you dont have cc and since most of pyro skills can just be avoided without linker you will be a sitting tank. you wont do any dmg with con, and when you transpose you will lose health
for pve, you dont have much grinding capacity as you would if u went linker. imagine your combo. aa on mobs to group them, swell size, fireball to hit 3, flame ground to hit ~5 while you jump around keeping them in the magic circle. going pyro 2/3, linker, and thauma 2/3 would help a lot.
anyway if you want a boss killer you would want to focus on world bosses because thats where the money is at. this means
pyro, linker, warlock, maybe sorc
psycho cyro linker warlock
pyro 3 sorc 3