Banshees don’t die so easily so long you have fine control of Micro and attack alongside the infested.
If you are talking about IL when they are at full upgrade, you are right and they are very tough.
But unfortunately their Cloud form only lasts for short period.
I made some adjustments to it.
https://us.forums.blizzard.com/en/sc2/t/improving-stukov-infested-liberators/13280