[2021] So what's the point of Supertesters again???

@The_Ruleset_Difference and @Chobittsu are correct: the Supertesters do FAR more than just help WG to balance new ships.
Entire new concepts like submarines and Superships require vast sums of data to be collected to really parse out how things work and see how they affect the game results. There is an important aspect to this that you're likely missing (OP) - that Supertesters are, on average, better at World of Warships than the average player.
The game has to be balanced for the sub-500 battle tater just as much as it must be for the super-unicums. With something like submarines or superships that do have the potential to be paradigm-shifters, we gotta KNOW and that means having the populace take a stab at it.

The difference is that we can pull them for a while if need be to make changes.

I have no idea what this is supposed to mean.
If you are trying to say that bad behavior in public games somehow compeltely invalidates testing in randoms, then I suggest rethinking the question.