I'd prefer if development focused on adding more ways to deal with it. To use a game analogy: we're playing Barbarian Hordes mode Civ4 with no Warrior unit. Given the disparity in power between certain units like Umberdroths and what you can build in the first several turns it's rather impossible to do anything about them when they do appear, even if you're being very careful about triggering them.
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Solutions may be:
Early +Defender numbers building option.
Spike Walls or other defensive buildings which your puny militia could hide behind. Traps in general might be both useful and fun, with placement being done prebattle.
City Defender specialty troop traits that only work if garrisoned in a city. Possibly just copy-paste the effects from the Defensive civilization trait with a labor cost.
Monster Slayer troop traits that help specifically against non-fallen/non-human enemies. A way this could be implemented is ignoring a certain % of defense (like spears) and group tactics which guarantee that only 1 unit in a group can die from a single monster attack. Although maximum killing of a single unit might be a good idea in general given the pacing of combat vs super units. Then certain weapons could provide "Cleave" effects and add more specialization to units. Most spells could probably do without that restriction though, which has the side effect of making damage mages juicier targets as is typically their role in battles. It also means that assassin classes are better used to actually assassinate important units (already in-game with champions/sovereigns) instead of going toe-to-toe with massive armies.
More/better traits to fight off higher power units. Possibly switch Underdog to +2 Attack per level difference? Although really what may need to be factored is effective Labor Cost (might be a problem for monsters) as raw level seems to do little for units besides grant a HP boost.
Upping the Squad type's unit count.
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With even a few of the above the early game would be changed drastically because building defensive units would be viable instead of a waste of time that could better be spent on either pioneers or building improvements. Not only viable, but possibly necessary depending on the aggressiveness of enemies nearby.
