Right now if you vote for a third party in the US your vote is wasted.

Under a ranked ballot system you can vote for a super marginal party confident that your more mainstream preference will ultimately get your vote if your marginal candidate loses.

This encourages votes for smaller parties

Are you saying more parties crop up? I still have third parties on FPTP ballots.

My vote in MA is not mathematically meaningful today, as you could correctly call the 2020 presidential race for blue back all the way back in 2016.

Change the voting process and I could vote for Party Q, then F, then D and have something closer to my true preferences be measurable vs today and give the parties a sense of where they stand with the populace. I’m still not convinced it breaks the binary star in US politics.

Right now, if those are my prefs, I have a choice of voting Q, voting D, or staying home. If Q is a third party, there’s an argument that vote might as well have not been counted or cast (because from today’s voting you can’t infer the true level of support for Q because some Qs cast their ballot for D just on the off chance that R would otherwise win; for the same reason, you can’t tell as much about the true R or D support either).

My question was around the size of the ballot, not the weight of a person's vote.

More third parties become reasonable contenders.

You have to rank them against one another. 10 candidates, 10 comparisons. 100 candidates, 100 comparisons.

Alternatively cardinal systems scale trivially (you express how much you like an individual candidate -- independently-- not how much you like a candidate -- comparatively -- to another candidate). You can bullet vote a party line if you really want.

That doesn't affect ballot size. You have the same number of candidates with boxes next to their name you put a number in, unless someone is making the implementation more complicated.