If i were to provide a more useful response though....
As someone that spent roughly a year farming dark almost exclusively, i dont care what level walls a th9 has.
It is still going to be infinitely easier or cheaper to alleviate a th9 of dark buried in the core, than trying to snatch it from between a pair of discos.
Everything else, you decide, but big walls are only helping once youve got something to slap opposition troops with while theyre trying to break them.
Just go to TH 10 when youre ready
well put it this way: i went to TH 10 after getting all legos because I just couldn't take it anymore. If I stayed and farmed heroes/walls I would have just ended up quitting the game. Too boring just farming walls over and over again