As of now (2.35), there are some units that probably have too much recruitment, which might pose problems for accuracy or gameplay in general. This list probably doesn't cover all of them (mainly focusing on western factions), just some I've noticed.
-Balearic slingers: These are the most notorious (and have been already noted in other threads). As a player who plays Carthage a lot, I've noticed that once you get the reforms you are always drowning in Balearic slingers. These guys, even outside of Iberia, are available with 3, 4, even 5 units in a settlement. Considering that historically the Balearic Isles weren't that populated and that there could only be a couple thousand of these men at most, having the capability to make armies of these slingers seems silly. Generally only one unit of slingers is available in a settlement, and due to the limited nature of these slingers it should definitely not exceed this in settlements outside of the Balearics.
-Gallic Noble Cavalry: With a confederation, you can get two units of these cavalry at a time in one settlement. The problem I've noticed is that once I've captured Gergouia/Bibrakte, I never need to use light cavalry again. Although they cost quite a bit more, the economy is good enough that it's not too crippling. I think that these should be restricted to one per settlement. They also appear in the Belgae allied state settlements despite not being in any other allied settlements (were they a placeholder for the Belgic medium cavalry?).
-Belgic medium cavalry: It may be just me, but I've always thought that the armor they've been equipped with warrants another armor point. As far as recruitment goes, three of them can be recruited with an allied state (along with a Gallic Noble Cavalry). That's a lot in one settlement, I would think it has at least one too many (and perhaps the gallic nobles should be removed). It's also not available in the other Belgae populated settlement (Nemetokena), which is a bit weird.
-West Celtic Light Cavalry: Not really recruitment related, but they have free garrison upkeep which is unusual for cavalry.
-Liby-Phoenician units: By the mid to end game, a carthage player is able to recruit two of each in the main phoenician settlements with the council administration governments. They are both good units (and will get better if the liby-phoenician cavalry get the extra point of armor) which is good for the player, but I was under the impression that liby-phoenicans were rarely used outside of Africa. Having in one settlement leads to situations like my current campaign, in which I can get an endless supply with a little management. They should be a limited population, and should probably stay at one. It might also be a good idea to limit their recovery to prevent overuse.
-Libyan cavalry: As of now, the number of them is kind of ridiculous. There are 6 in Qart-Hadast and Atiq by the mid to late game, which is kind of excessive considering you can also recruit two Numidians and two Numidian nobles as well. Currently this unit isn't very good so the amount doesn't matter as much, but come improved armor (and perhaps other armor) and the removal of Carthaginian noble cavalry this unit will be a lot more important.
-Other Libyan units: There are a lot of Libyan units available to Carthage. This isn't necessarily a bad thing, but it means that Carthaginian players rarely need to consider manpower. I never need to use numidian infantry or import iberians since I have so many libyan professionals.
-Numidian nobles: Getting 2 (in the late game) each of the core African provinces of Carthage means even after I exhaust my Liby-phoenicians, I still never need to incorporate lower quality units. Especially considering how good Numidian nobles get, I think they should be limited like the Liby-phoenicians.
-Equites: I guess spamming high quality units is sort of the trademark of Rome, but there are too many equites. With a Latin constitution, you can recruit more units of equites (5) than any of the infantry classes (4). The number should probably be dropped by one or two.
-Triarii: I've stated this before in other threads, but I think the unit size should be increased by 1.5 (to 120) and upkeep adjusted, since 80 (one the largest setting) is a bit too small to use effectively. This would also mean a decrease in recruitment. This is less historical so I doubt it will be implemented.
-Greek Elite Hoplites: In the later game I've found that higher level governments allow the recruitment of two elite hoplites. The problem with this is that the available distribution of those governments is very widespread. This can lead to entire armies of these troops being available, and I'm not sure if this was intentioned to happen.