Its hard to say, if there is alot of rotted wood, then its worth it. If the wood is in generally good condition i see no real reason to invest more money for a full frame tear out. I just installed Okna 800 windows which have the best air infiltration number in the industry but still went the full frame tear out due to their being so much rotted wood. Most homes do not need a full frame tear out, just replacement.
Just so you know, the elements and sunrise vanguard or restorations have much better performance numbers than both marvin and pella.
The Okna " enviro star" 800 series is is on an even playing field with the elements.

No problem about the questions.

Unfortunately, the time to do a full tear out and full frame (new construction) replacement was when you were doing the siding.

I know that is Monday morning quarterbacking in this case but that is the reality of the situation.

How does the company propose to seal the full frame window and tie it back into the WRB (Weather Resistant Barrier) layer in a full tear out application?

The only proper way to do it in my opinion is by removing the siding and pulling in a nailing flange window.

If the window is not leaking at the window frame to wall framing connection, you might be best suited to leave that connection intact and go with an insert application.

The installer can drill holes in the window frame (old) jamb sides and inject foam to try and seal up the opening around the window.

Even perfectly sealed in that case, it will not address the air leakage in the wall in general (from areas other than the window connection) and where it will come out (most often around the trim as you are feeling now).