Well, I was pushing my point a little too much. By the end of the war, true enough, the Earthling cruisers were the backbone of the Alliance fleet. But still, they were not very good, and they were effective only by their sheer number (and because they had so much nuclear missiles in stock
Humans fought bravely in the war, producing a relatively crude but numerous and flexible fleet that fought on multiple fronts, while also providing many officers and crew for allied fleets. Those who had chosen to maintain the Peace Vaults in the first days of the Peacekeeping Army were vindicated; even the Chenjesu were shocked by the total destructive power represented by the sheer number of the old alliances' nuclear warheads and the United States' half-finished orbital laser defense systems. Primitive as they were, refitted for ship-to-ship combat they became the reliable and ubiquitous weapons system of the Earthling Cruiser
Still, they did really major mistakes :
The speed with which Humans were thrust into such a perilous situation without even a basic experience in dealing with other sentient races may have contributed to such diplomatic blunders as the disastrous Human/Syreen crew exchange, an accidental human attack on an Arilou fleet, and the Great Insult that poisoned relations with the VUX. Nonetheless the Human industrial base became crucial in the war effort...
I said there were the like the Italians of WWII because they brought two new enemies to the Alliance (Androsynth, VUX), but for their skill, they're more like the Romanian in WWII : sheer number over quality (between 1/4 and 1/3 of the Axis troops on the Eastern front were Romanian I think).
While the cruiser is pretty effective to damage an Ur-Quan Dreadnough (until it can close in, then the Cruiser just go BOOM) or a Spathi Discriminator/Eluder, there are few starships he will actually destroy : the VUX ship, provided he survives the ambush, and the Umgah Drone, except if the pilot is good (and lucky) with the retroreactors. It is supposed to be - and is - one of the weakest ship of the fleet.
I take a Yehat ship anytime over the Cruiser in SC2. And an Eluder anytime against anything else.
Anyway, the Humans finally got crushed at the end of SC I 'of which I was talking about, although most of these events are only known in SC2). Too bad they manage to win again in SC 2 :/ I like the fact that it is almost compulsory to pilot a Pkunk (aka : the junkie of the galaxy) ship to destroy the final boss.