Nothing I know of can beat a Fully Upgraded Jarl in one on one comabat except Zeus' Mymidions, makes me marvel at why everyone keeps saying his underpowered, except to my recently drawn conclusions, judging my American Eagles post, and AgeMyth's response, I am surrounded by morons. Simple as that, however, I would like to mention something to Deathshrimp:
It's not Jarls that we have a problem with, it's Odin's Jarls, these guys can kick a non-infantry unit such as (sic)Prodromos' ***, and then regenerate after! A big pain, but this proves it's not just the infantry that need fixing.
Like you say, Spearmen are Cost Effective, I have no clue what people are talking about there, as for hoplites, unless I am mistaken they were never intended to counter cav as the Prodromos, but to be a common infantry unit for the Greek civ. The only problem with that, would be the fact that the hoplites more expensive than a Hypatist, and Ulf's likewise are to weak until Heroic, and only then if you worship Bragi and have gone with Loki, which means the only really good civ that can use it is Loki.
The Ulfarsk itself seems to have a lot of thought put into it. They counter Egyptian scouting by getting a bonus vrs obelisks, for instance, very helpful in Archaic and early classical, it lets you keep your forward base hidden.
All Im saying is it's not necessarily just the Infantry that has a problem.
On a much different topic AgeMyth should get a warning, at the least.