I was very struck in Astral's let's play (episode 11) that the tactic of build-archers-cos-they-are-cheap-then-immediately upgrade-to-archers is effective but cheesy.
IMO costs (or upgrade costs) need to change to make this less attractive unless you are really rolling in cash - i.e. - at least one of:
1) AtlAtls should be more expensive (probably)
2) Archers should be cheaper (doubtful)
3) Upgrade costs for units should be higher. This is defined by UNIT_UPGRADE_COST_PER_PRODUCTION which is currently 1. Making it 2 would be far too much, so if we want to tweak that we need to change it to 100ths or something
IMO this case is mostly (1), but maybe we should consider a little bit of (3) also...?