each individual user's "swap-weight" (the plankton must be able to grow vs. whales shouldn't be able to play the market I mentioned earlier)
[...]
each individual user's swap-weight (which would scale linearly from some bigger number like 3 or 5 for the tinyest deposit and some fraction like 0.2 for the biggest whale on the swap market
I think this is a big obvious flaw in your plan - you're relying on a 1:1 mapping between people and accounts to identify "whales". If the rewards from the swap market were 25x higher for small holders as they are for large holders, I would bet my last dollar that every 'whale' on the platform would immediately seek to open dozens of separate accounts to split up their balance and get the beneficial rate.
Besides that... what exactly was the ideological justification here? Seems rampantly unfair to treat one guy's invested dollars differently when they all serve the exact same purpose.