As for the Moto Proprio, they didn't ask for the Moto for the SSPX to be able to say the mass, they asked that the Mass be freed for all Priests without penalty. basically a declaration. All of these were conditions for the SSPX to talk with Rome about a deal.
Essentially, Rome came to the SSPX wanting us to join them, the SSPX stated that they wouldn't even consider it unless 3 conditions were met.
They fullfilled them, though as you say, they did so on their terms and not in the way the SSPX envisioned. But it is what it is.
As I stated, I am not in favour personally of a deal unless Rome converts in full, but I am always in favour of attempting to convert them and anyone else, but especially them because the result of that would be an end to the Crisis sooner rather then later and thusly the Salvation of more souls.
Edit: Of course if Rome converts in full then the SSPX disbands as per it's mission.