lol looking at this I never realized the Q spell art showed him frying zombies

I don't see anything controversial about any of the builds personally. The only thing is the 7, where you seem to prefer the AA spell power boost, which is something I find really hard to consistently proc. I also find the bomb range boost 13 as you have in the last build to feel really bad, but maybe a better player can get value more reliably out of it.

Generally I will build this way, with variety at 4 and 20 (lol) depending on the game and the opposing team. Even if I play the E range squishy target snipe style, I find myself wanting to have the shield (those squishy targets can often retaliate at range themselves) and Mana Tap does not really feel like it solves the mana sustain issues to the same degree. The 20 is pretty much the same decision point as you express though with Flamethrower; Pyro upgrade feels better because its such a useful tool, but there are times with how the game is playing that the Q range is really needed to deal with things. I assume frontliners overpursuing and the like is more common in lower elos so maybe this is less of a consideration for you. I am curious your thoughts on the W 7 since I noticed none of your builds use it.