Vikings are literally DIRT CHEAP you should not be even complaining about anything regarding vikings until you come to terms with the fact that they are absolutely DIRT CHEAP.
They are fodder practically with nice long range that if you even bother to micro parasitic bomb is not going to make a difference.
You simply click and pull out a viking and on top of that terran has the usual over powered ability of dropping mules literally in the time of need that can repair them on site and why use mules when at that stage of the game you should have TOO MANY SCVS which means you are looking for excuses for them to die so you could have 15 scvs repairing them.
Need I remind you that REPAIR IS STUPID AND BROKENLY OP IN SC2?
At the end of the day parasitic bomb SHOULD BE GOOD VS VIKINGS.
It sure as hell is not good vs those high health and over powered battlecruisers. Which when massed are just going to EZly walk over everything zerg has.
Combine repairing scvs/mules with Battlecruisers and you got an unstoppable killing machine. They will kill everything including corruptors.
But JUST IN CASE… YOU GET OUTPLAYED…
THE EZ MODE RACE AKA TERRAN
CAN WARP BACK HOME WITH THEIR BATTLECRUISERS!