I was surprised as well. When the fall of Ermor was near, I already planned to quickly strike against monkeys, as Executor predicted. So I assembled 2 new armies, moving some of the SCs from Ermor front before finishing the war there (western army), and summoning some more in the cap (southern). Fortunately the jags are still useful with proper buffs even in that stage of the game, so my main concern was to prepare 3 sets of army buffers and 2-3 support SCs in each army (I had enough forts and money from constant expanding to quickly produce enough jags at any place of my empire). The third army was planned to appear with gatewayed soldiers from Ermor front and 3rd set of buffers, but unfortunately I lost too much during the last storm so I had to delay it somewhat. In the end I just teleported it to the sieged castle to help defend it (the buffers were already there).
I think the main mistake Executor made was to allow me to BH in all my provs without much interference almost till the end. In fact, in the end, when he had less resources but started to actively cripple my blood income, I went down to 60 or so slaves/turn from peak of 200+. So I was able to sac 5 slaves in most of my castles + send 9 or so lesser horrors each turn + summon bat spammers. I made some tests and 8 big Horrors were enough to take down single Treeant equipped as Executor's. But mainly I used them as raiders. Buffed jags + SCs were even more successful than I thought, so I moved through his lands like a hot knife through butter. And, after Blood-9, it became sort of one-sided game, with banishing anything worth banishing with 10+ sun priest parties.
Executor, now I'm satisfied. My fall in Timewarp is revenged
(It was a CBM 1.5 (with gemgens) game where I controlled about half of 250 prov map as LA Ctis and still had to surrender due to his gemgen-fuelled globals and some mistakes).