So this seems easy to solve by computing "work" in a smarter way.
This smarter way may open the system to Sybil attacks if it removes "linearity", splitting/merging/recombination of transactions may give adversary an advantage in this case.
I also want to get rid of the target difficulty and simply combine whatever hashes show up.
Without difficulty you don't know if someone did a lot of work or just was superlucky (and got a lot of leading zeros).