I understand that a lot people don't really like Shock cavalry overall and, while I must also note that I never play on Ultra (only Large) I fail to understand why are Dragon Princes criticized so much s being pathetic.
Yes, their starting stats may be a bit poor, but with upkeep reductions you can field a lot of them and a little investment (Lord skills and techs) their statistics are nearly godlike.
With no temporary buff from any item, ability, ritual, Hero trait or spell whatsoever, with 61 Melee Attack and 66 Melee Defense they are more than OK for a shock cavalry unit that stands at an amazing 101 speed. Their 46 Weapon Strength is a bit on the low end, but their 121 Charge bonus (sic!) is nearly godlike. That's wiping almost everything that doesn't have expert charge defense. And the -50% Vigour reduction is quite excellent for a unit that'll be maneuvering the battlefield a lot, not to mention outlast most hostile units.
This is even better with the two rites if you really need a punch, Eldrazor's invocation bringing their MA up to 71 and WS bumped up to 57. Their only problem seems to be a bit low AP damage (14 or 17 with the invocation) but considering how impact and charge bonuses are calculated (both speed and CB being literally over a hundred), that should not be that huge of an issue if they don't stay entangled for too long with armored units. And the Greater Invocation of Vaul gives them flaming attacks which is absolutely incredible if you play as Imrik you get a lot of Fire Weakness maluses, theoretically pushing a unit to an almost 90% fire weakness (20% from Imrik's passive Ashen Fields, 22% from the Flammable effects, 22% from a firewizard's Kindleflame passive and another 22% from the Handmaiden's Entangle ability). And the princes even cause Fear.
But where they really shine besides their incredible speed is that they're actually pretty tanky. With almost 5000 hit points (more than any other High Elf cav), 40% physical resistance and 145 armor (150 with Vaul's ritual) and the fact that they are shielded (35%), they easily outstat the Silver Helms and are one of the strongest shock cavalry units in the game.
And just imagine boosting them further up with a banner, an effect or a hero that adds a bit (a couple of points in MA may not be much, but everything helps). They are quite awesome and their 90% fire resistance means you can freely play around with aggressive Lore of Fire spells (a lore which just happens to be one of the strongest in the entire game) and the dragons' breaths. A flaw may be the apparent lack of magic resistance (with only 5% Ward Save).
P. S. On a side-note, Imrik should really be able to get Forest and Black Dragons. With Drycha and Rakarth now, there's no reason that they are locked while their unique legendary variants are available to him.