Without going into my entire titan strategy, these are heroes I have maxed:
Horghall, Joon, Athena (3rd tier max), sartana (3rd tier max, havent used her much yet), rigard, sabina, grimm, gormek, scarlett, melandor, boldtusk, wu (but yeah without him). 50k is a nice score, but can also be gotten with different teams with proper strategy and items (not to even speak about stacking guardian event heroes with normal defense debuffers which I don’t have either).
2 Possible teams: (blue titan) Joon, horghall, mel, sabina, athena (80k yesterday and 60k/hit average) / (red titan) athena, grimm, scarlett, joon, rigard (average of 50k+ per hit)
Wu can be a fun part of the puzzle, especially to ‘freestyle’ against low level titans - i won’t disagree with that. But he is not nearly as necessary to good titan scores as any of the damage debuffers and doubling up on strong colour. What level titans do you usually hit? As I would probably agree that if you hit below your level he can make a bigger difference.
I use wu almost exclusively on purple titans (in a strategy that depletes a crapton of items) and while I do get very high scores there (this is also related to titan stats and item usage) - my titan hits are generally pretty solid and generally in top 5 in a top titan alliance.
The heroes mentioned by @Fledoble are with reason and as you say, look at Overview of heroes used in defense teams of top 100 and you notice that those heroes are disproportionally used in defense teams.
I do use wu, and i would trade my wu in for lianna on offense.