They can't file a DMCA counterclaim because they never received a DMCA claim in the first place. Youtube simply blocks the content, you don't even get a proper claim with the contact info.
"They would then be required by law to reinstate the content. The step after that would be that the other party now has to go to court, to take down your content." is the followup process for a DMCA claim - but that's not what's happening here. Youtube is not requiring claimants to submit a DMCA claim (with all the associated process) and they are not submitting DMCA claims. Youtube could make their copyright claim process following these rules if they wanted to be on the side of users, but they have not. They can also choose to have a process where any complaint simply causes content to get removed with no recourse, and this is pretty much what they have done.
Also, for many people, even doing something like "sending an email to counter claim" is too much work for them to bother doing it.
You'd be surprised how many people won't follow through on something when there is even the smallest barrier to them doing so.
> And why haven’t I heard of this before in all these topics?
Things can get to be pretty technical, when people are talking about the minutia of a counter claim to DMCA. It does not surprise me that info like this is not well known.
But we are not talking about the DMCA system. We are talking about YouTube's own system that is not DMCA and for which they are not required to provide due process.
Not through their fake on platform system, but instead through their "official" counter claim contact info email.
They would then be required by law to reinstate the content.
The step after that would be that the other party now has to go to court, to take down your content.