I can agree with the point that eating the adc at the wrong time can be fatal, but I feel like the point still upholds that Tahm needs more of a drawback. It's not that hard to stick close to the adc in a teamfight, and W when they're in danger of being cc'd/combo'd. Especially when cc skills can be so valuable in teamfights.
Personally though, I can't really think of any good method to balance that issue without gutting it in general. Perhaps when Tahm spits his teammate out, they get a small debuff (covered by saliva maybe?) that applies a slight decaying slow to the spit out target for 2 sec, so that Tahm also has to think about where he's going to spit them out. Right now it's pretty much a free Fizz E for the adc, so long as the Tahm player knows what he's doing it's a tier 1 get-out-of-jail-free card, and can also be spit out across walls through either's decision.
That or maybe Tahm doesn't get to choose where to spit out the eaten target, so it's up to the ADC's skill/interaction.