in sp 2 things assure you win in the lategame :
- your mentioned clamming
- real bloodhunting as a blood sacrifice nation .
just build hordes of vampires and dominionpush .
the ai can't cope too well with this
sc's are good too of course . but even against the ai later you need to give them perhaps an army as assistence . because swarming + some highlevel toys can be a danger for many scs . so lategame even the ai can manage to take out single scs .
all in all i think on faerun with impossible ai settings some ais get quite large numbers and give a nice fight .
if you can bring up utterdark + other extreme damage spells though the ai has almost lost .