You misunderstood me. I was using what happens now as argument to explain why they wouldn't join you in the first place in the scenario that nobody knew the tadpole was a problem.
Maybe there's no tadpole magic telling Karlach isn't what Mizora says she is, but other companions (At least Shadowheart and Lae'zel) do point out that Wyll is full of shit accusing her of being a devil.
Wyll might see reason, hard to say. He and Karlach are the most likely to still join you. Though if Wyll didn't know the tadpole was a threat, he has no reason to stay after killing or sparing Karlach.
Astarion is still looking for help regarding the tadpole, though I'll admit he's the easiest to pass up on when he tries to bite you, at which point he assesses himself as a willful threat to you.
If he does not know the tadpole is a threat, he will not look for help regarding it. He has no reason to. In fact, he will actively oppose it. The tadpole helps him.
Lae'zel is still helping you, that she's doing so reluctantly is irrelevant.
If Lae'zel did not know the tadpole was a threat, she would not seek a cure, and therefore not need you at all. She will fight you or ignore you.
You don't know the gravity of Gale's issue until you're already on better terms with him than at the start, until then you just had to feed him some magical items every now and then, and there's plenty of garbage that counts for that criteria
Gale has no reason to join you if he does not know the tadpole is a threat. He will either admit his issue already, or go on his own way because you're not an elder wizard.
Yes, Lae"zel and Shadowheart will want each other dead, but them attempting to kill one another tends to happen pretty close to Act 2, until then, it's still two people with a similar issue.
If neither of them knew the tadpole was a threat, the only thing they would care about is the artifact. Lae'zel may not know Shadowheart has it, but Shadowheart killed Githyanki to get it and will never team up with one to protect the thing she stole from them.
Also if you're pointing out Wyll wanting to hunt down Karlach before anything, I think there's the other issue of putting your personal problem before anything else is also bad as it throws you headfirst into the patrol and the creche at level 2 or 3, for another topic, but still, game heavily suggests you help other people - also you can tell Wyll you'll still prioritize the tadpole and he'll still tag along.
The thing is that if nobody knows the tadpole is a threat, then it's not a personal problem. That's why they wouldn't join you.
For the game to work out, everyone except for you needs to know it's a problem. Why else would any of the companions seek a cure? They all have massive personal issues to deal with that are a lot more important.
