FYI I'm not an expert but I do know a thing or two about bass and pond ecosystem. The more bait you put in the water the better the bass will be as you know. Seems to be a good food chain as is right now. Depending on when your f1s and floridas were stocked my guess is they were consumed by your existing northern bass, assuming you stocked those florida bass as fingerlings. Thus why the growth across the board is not on par with Florida Bass potential because the pond is probably 99% northern bass genes right now. Though as you said a pond with 6-7lb northerns is not too bad.

However we all want bigger Bass so:

If it was me I would bring in a good amount of f1 or florida bass fingerlings this summer, enough so that some evade your existing Bass, and hope in the next few years those new fish get to trophy size. THAT is when I would bring in the gizzard shad once you know you have some REALLY big bass in there.