I'm not sure that teching speed was your problem. I think it might have been just a little too fast, but one of the other big problems was the major loss of footmen you suffered fighting the spiders earlier. I'm not sure why that battle turned out quite so poorly for you...I've taken on those spider clusters before and not lost nearly so many men. Maybe I had a few more footmen before I tried taking them on, or perhaps they had an offensive upgrade.
The one thing I noticed about all of us (myself included that game, I usually do a better job of it.) was that we didn't have enough troop producers. By the time the big battle started, we had a total of five active troop producers among the three teams, and that isn't nearly enough for online play. The only races I've found that should stick with just one of their initial troop producers is the undead and the orcs, unless they intend to use those buildings throughout the game. Ancients of War and Barracks both produce good enough troops that a double count of them early on is very justifiable even if you plan to go on to something else. Teching straight to X unit is another matter, but that's a gamble that the team can decide to take together.
I'm not sure why, but we were also missing Fell for the major conflict. He came in, but only after my army was completely gone, and I think Pleasington had about one knight left. One thing I've found in base defenses is that it's often best to let the enemy chew on the base just a little bit while you and your allies get coordinated for their jump back to the base that's being attacked. Under the firepower of three or even four enemy battle groups, one or two friendly armies are almost never enough to turn the tide. We didn't do that and we paid for it.
I also made the mistake of trying to use night elves on the front line of the battle. I should have been shooting over the heads of Pleasington's forces. Huntresses, incidentally, can throw their moon glaives over the heads of footmen and ghouls...maybe knights and grunts too, and should usually be behind them in battle to focus the total team firepower.
One thing we might want to try out is having all members of our teams tech striaght to high level units, gambling that the enemy won't attack early, and use our heros in one big pack to creep together. Six heros is a formidable creeping force, particularly if they have spirit wolves and/or water elementals available.