This mod seems like a good starting point for addressing this longstanding issue, and I hope the community will give it a thorough testing. Personally (and without having tested it) I think it could probably be weighted even more heavily towards buffing melee, but that's just a baseless gut feeling (which others might call a prejudice). Specifically I think the most historically grounded representation of the melee infantry would be to give them both insanely good armor, and equal or superior DPS, compared to the ranged infantry. Read what's below to see my reasoning.
As to how things ought to look:
I agree with @chrstgtr that the time tested solution to this exact problem, used by almost every other RTS on the market, is to always make melee units faster than their counterpart ranged units. It works on a mechanical level in a way nothing else under discussion can so it's an appealing fix. This we must grant as axiomatic.
The problem is this conventional solution butts up against the actual historical record just as hard as the current ranged-unit dominated meta. The melee units under discussion represent heavy infantry and the ranged units represent light infantry. Heavy infantry are NEVER going to be faster than light infantry in any pre-industrial context because of simple physics. F=MA, and heavy infantry will always be carrying much more M for roughly the same amount of F generated by their muscles.
My understanding (though perhaps others feel differently) is that the weird way this tended to work out in history was melee and ranged actually had little direct strategic effect on each other most of the time. Ranged (ie light) infantry were agile enough to evade any direct confrontation with heavy infantry that they did not want. Meanwhile heavy infantry armor was so protective that ranged weapons actually inflicted no meaningful casualties to them on the time scale of melee combat. Of course if the heavy infantry stood around getting peppered for hours (like if the ranged units are protected behind fortifications, or were using hit and run tactics on an open field) that is an entirely different matter... and one we can simulate.
Thus the role of ranged infantry then was a) to annoy the heavies when they could do so safely b) kill other ranged infantry that cavalry could not safely engage c) zone away enemy cavalry (especially the ranged sort) that might be trying to flank around friendly heavies without joining into melee range.
Heavy infantry's role was to be pretty much the only cost effective DPS source against cohesive enemy heavies during pitched battle. They were also unmatched when the enemy could be forced to fight, as if they were protecting a town or some such. A lot of the way light infantry or cavalry actually went about decisively beating a heavy infantry force was about disrupting logistics or morale rather than causing direct casualties. Unfortunately that is hard to simulate.
If this interpretation of ancient combined arms were brought to 0AD it would admittedly look really weird. A lot of battles would be just lines of heavy infantry duking it out, this is true. Ranged units would only be used in a few very specific situations: when protected by fortifications, when supporting a melee fight in a very tight choke, or for conducting or countering harassing actions in no-man's land when no enemy cavalry are present.