The biggest problem for recon units is that they are never a cost-conscious choice for military capability, which means late-game recon units are almost never built by players, and only occasionally by AI.
The recon tree would do fine with a tech-cost reduction (especially Hunting, which is insanely expensive and doesn't even get researched early by AIs that really ought to; i.e. elves) and making all of them illusory so they simply couldn't eliminate enemy units on their own, but giving them much-improved mobility by having them ignore terrain penalties to movement.
That completely changes their functionality, but makes them an excellent complement to mounted units. In fact, it gives mounted units a very strong strategy in complement, which is better than it currently stands with a handful of mounted units being used to flush out enemies within your own territory and harass individual enemy units traveling just outside your territory, for the most part (if you bother to build any at all).
Guardsman should be removed from most of the melee line, but consider that a certain leader grants it to all units (and, indeed, is one of the major reasons to choose him) and you'd essentially be adjusting those races' potential power. Not a bad thing, by any means, but something to keep in mind.
Archers are essentially fine. They are second-rate attacking units, but first-rate defenders. With a couple of city defender promotions, they can turn back even mithril-equipped champions, so they hardly seem to be a poor use of hammers.
The real trick to the whole mess, of course, is that heroes tend to be overwhelmingly powerful when compared to regular units. It becomes even more striking when you compare them to top tier units. How often would you risk a well-promoted national unit against Duin? You just throw fodder at them and hope you have enough, usually. That lends itself very heavily to the melee line.