Useless techs and units? Umm...
1. Farming sux, so why bother getting the farm upgrades? Anyway they don't help very much, you'd need a huge farming operation for the upgrades to be worthwhile. Solution: Add +0.05f/sec farming rate with each farm upgrade as a "signing bonus". While not enough to make farming as good as other food sources until all bronze age market techs are researched, by which time other land food is usually gone, it would still help and the farm upgrades would be a must for any farming operation.
2. Cataphracts, one of the most expensive upgrades, and one of the most useless. They were already bad in AoE, so naturally scythes were added to do everything better! Solution: Give them higher armor and shielding like historical cataphracts, 7/3 sounds about good.
3. Heavy Cavalry? LOL! Read above and add camels to chew them up. Solution: Give cavs more usefulness so they're worth using even after camels are out, maybe by giving them an anti-archer bonus. Hmm, or move the hcav upgrade to bronze and fix two problems at once.
4. Jihad makes your villies work less effectively. Siegecraft is a must, but I find jihad just isn't worth its downside, since with an unreduced econ you could simply produce more military and villies. In DM, where they are used more as field engineers, I guess it might have some use. Solution: Change the work reduction to half what it is now, and it probably becomes worthwhile.
5. Impies are rarely trained except to turn into compies before the compie upgrade is done. They aren't as good as compies, and cost gold unlike bowmen. Solution: Make them an upgrade of tool bowmen, with the same food/wood cost. The impie upgrade would still be required for compies, but impies wouldn't make the change.
6. Short Swordsmen are useless the moment they're faced with virtually any bronze units. Solution: Make them available immediately in bronze, like cavs and camels. They'd be far from bad vs tool units, cheap and fast to produce so you can make many quantities of them, so not a bad early-bronze rush overall. Improve broad swordsmen and suddenly they have a future.
7. Broad Swordsmen with all the upgrades can defeat compies 20 vs 20 (on flat, open ground with no obstacles) but barely, and require so many upgrades that it's not really worth it. Like all infantry units, they're highly vulnerable to anything with range. Solution: Insta-bronze short swordsmen (see above) would cut upgrade time by half. Add a wooden shield upgrade in tool, and archers might even need walls or cannon fodder to slow the infantry down a bit. More than +1 shielding would make infantry unstoppable though, so don't go overboard ok?
8. Tower Shield is very helpful to infantry, but unfortunately also too late to help bronze infantry and anyway it's pretty expensive. Solution: Wooden Shield, a tool age shield upgrade, which would complete the tool age pit techs set ( collect them all! ) making it similar to later ages. The new impies should be moved to tool to keep that age's archer/infantry balance. Might want to give watch towers and sentry towers +1 dam each, too.
9. The centurion upgrade is expensive, and phalanxes do a fine job especially if you use those resources you didn't spend on upgrading. Solution: Lowering the upgrade cost would be a possibility, but maybe someone has a better idea.
10. Wow, nearly forgot the watch towers and sentry towers. Towers are relatively cheap for iron age economies, but they are far too expensive (except the roman ones) to be massed earlier. They are used offensively in tool but don't help much for defense. Any attempt at improving towers are instantly flamed by ballista tower haters, who claim (and I agree) that ballista towers are already a pain in the axe. Solution: First, split ballista towers from the rest (loud cheer heard in the distance). Next, triple the RoF of the ordinary towers. Then, double ballista tower damage (up to 40), *but* give them a minimum range of 5 (!) and don't give them the benefits of ballistics.
Well, that's the top ten I guess.