Ok in terms of master plans, that one was solid! The idea of using the teleporters to sneakily assimilate all of starfleet is insidious, genius, and just feels so Borg.
It also showcases that this plan was not all or nothing. Now sure from the villains perspective, grabbing all of starfleet in one go is the absolute optimal solution, but even if that hadn't worked, you can see scenarios where they could have grabbed ships more slowly, or still gotten the majority of the ships in one run and then taken out the others. This was a plan long in the making, and it could have easily been pursued in a number of different ways. That really shows the intelligence of the villains on this one and I appreciate that.
Now the question does come back up....why did it HAVE to be Jack? Now sure he has the seed, but is that really the only seed the queen would have planted? Could there not have been others? Or perhaps Picard did in fact have irumodic syndrome and part of that was why Jack works as well as he did, or something something. The problem is, there is nothing about Picard's experience that feels unique enough that it had to be Jack. The Queen could have done a locutus on millions of individuals and waited for proper children.
One thing this highlights....Picard is truly an inexperienced father, and really botched the interaction with Jack. The one thing Jack couldn't' stand was being abandoned, being alone. If Picard had hugged him during that scene, and said "Jack you have to go, and I'm going with you, I will be there with you every step of the way".... Jack might not have gone rogue. But ultimately Picard is truly starfleet first, father second....and it was that moment that shown through. That is honestly very in character for him, so I don't mind it. People could argue that Jack going rogue seems crazy, but honestly we have no idea how much influence the queen has at this point. The last opening of the door + feeling like his family has turned against him could have snapped the last bit of resistance left, and so off Jack goes.
While the "under 25" thing may seem a bit convenience, there is enough science behind it to be plausible. There are many genetic therapies we are looking at now that would work on children but not on adults for that very reason. Just because you have the ability to receive the signal, if the machinery hasn't been "grown" into you over time, it just may not have the roots needed to stick.
Having the changelings work together with the Borg is interesting. There is a lot of similarities, with a hive mind notion and a desire for totalitarian order. Combined with a mutual enemy in starfleet, yeah seems like reasonable bedfellows.
The Enterprise D as Georgi's equivalent of the "Hot Rod in the Garage" is perfect.
Now one thing I have forgotten from Picard's last season. Didn't Jirati become their new queen? Or was that a borg splinter cell or something I can't remember.