So lemme start by saying I tend to look for what a unit can do, not what it can't.
Lich super (prince)
Highly useful later on in mass rezing, skelle/locks for your wall, if your on a server that has pretty regular wars, its a choice between decent defence(high rez rate skelle/locks) vs good duel armies ( well researched scorps/spiders). I've tried a few times to bring the lich super to duels, it just cannot do much more then get wrecked once it passes your frontline scorps. Not bad, its got other uses, but I'd rate it as purely utility. You can also take it along on siege runs with opponents that have tier 10-11 golds, and get a good haul of free locks/skellis out of it, but this is pretty rare I'd say on any server.
Dawrf super (prince)
Best use is for bronzing, and helping to meet power req's, otherwise its sub par in a duel and takes up far too much room in a siege run, I do not have the personal experience of using the dwarf super. This assertion is just based on the high HQ dwarfs I know.
Rakkan Super (prince)
Again, another unit that helps with bronzing, the unit summon makes up for the massive area it takes up, and maybe you could make use of it in a duel, as those summoned units are not a loss to your main army. So in theory it could be used in silver dueling. However, the only rakkans I know are still in the mid to low 30's, harder to say whats viable in this big hq 40 duels without seeing stuff in action
Human Super (prince)
So heres the crux of my whole point here, going over the uses, which are mostly utility, to overall MEH, why does one race get a unit that rez's 30 units, it allows for no loss sieging on targets thats would normally cost you a couple thousand rare rez. Its not as if human tank is sub par, I'd argue its in line with all the other races, however I watch humans go in on targets and take minimal losses, and they got to do that 3 times a day, is this a limited area of their expertise, not even slighly. As the other 3 supers have very little use inside void, but the Humans super is what allows for perfecting a large number of the void allot sooner then the other races can due to that rez. Is that a huge advantage, not so much, however being able to no-loss siege is a massive advantage, one that should be looked at and addressed.