Now that blackrock stew is selling for as little as 5k/bowl, (the recipe now being available) the Bane Dragon will certainly come into its own. As noted it has better stats and casting ability than most of the limited supply of Dread Warhorses - few of which have good resists and mana - plus it can literally shoot poison out its backside. I discovered this less than charming capability when training one....you can't use the trick of grabbing up a bunch of binders in Old Haven to blast it into GM spell resist because it will kill them all with its back turned to them. I had not noticed this "backfire bomber" talent prior to the availability of cheap stew.
There are two problems with the Bane. First, getting a good one is painful. It took hours - and I mean HOURS - of farming them to get good ones. By "good" I mean mana well over 125 (like the Dread, it can go as high as 165), HP over 620, strength over 530, and very good resists. Their HP can go as high as 650 but that stat is the least important of the lot.
I don't want to calculate the time it took me to get two in the 4+ rating range. You're also having to do this farming in Slasher's stomping ground of the Abyss.
Second is training their magery. No matter how good you do you will likely begin with magery in the 30s, with eval and med only slightly better. Expect to spend 10 hours or more to GM magery on a Bane employing a Shadow Ely. Tricks I use are feeding it stew of course (only once every 24 hours will keep a Shadow Ely poisoned for HOURS and actually be able to put a dent in its HPs as its magery climbs), and buffing it to the point where some of its spells fizzle. This means applying Bless and Strength, beyond their ability to bless themselves, constantly.
When you're done you'll have a true oddity among UO pets: a combat animal more capable trained than it was in the wild. The Bane is not a divide by two pet to begin with, which helps.
I would also submit that the Hiryu is an extremely capable combat comrade against people. I think one of the reasons they're not used much is that people don't understand them well. They look for the wrong things.
Two stats, beyond resists of course, are keenly important on a Hiryu: intelligence and strength, in that order.
They do not cast but their intelligence (max: 325 prior to blessing) governs the power of their specials. Their chief special, of course, is Dismount. A Hiryu with high intel can dismount you in a manner that makes remounting impossible for an extended period. At max strength (705) you can go into combat with them at over 800 buffed with Bless and Strength. A high strength, high intel Hiryu will simply kill your dismounted self quickly.
Of course, the Hiryu cannot bless itself. You have to do it.
Hiryus are also natural dragon slayers, much as the Cu is a natural demon slayer. They are effective against Banes and Reptilons solo, and I've taken down Greaters with a Hiryu but only with vetting. These, of course, are my "pre-patch" Hiryus.
Pre-patch or no, an unaided, high stat Cu Sidhe will best an unaided Hiryu. The Cu is slow but that's a moot point. UO combat pets, unlike UO players, don't run away from one another
The whole matter of whether players frown your use of a combat animal or not involves a realm of abject whining idiocy you rarely find at such an extreme level elsewhere in the game.
Some players simply insist that something illegitimate was used against them whenever they die. That's a separate matter.
Others make an illogical distinction between a combat pet and other weapons, as if a Dread is somehow different than a bow or a sword. If you're attacked, bows fire on their own; swords swing on their own. If you issue the Guard Me command pets will attack what attacks you. The only difference is that the archer has archery and tactics; you have taming and lore. Both skill sets were obtained though tedious repetitive actions. This is more a cultural thing than a matter of reason. No skill, all kill...and similar nonsense.
Ultima Online, unlike a scrupulous combat or sports simulation, is not a game of skill in that sense. Rather it's a cumulative character game where the game itself bestows player characters with greater capabilities based on a combination of repetitive action history and load-out: skill points, and gear. If I have performed a given action enough times, and am equipped with items complimenting that action, performing that action "in anger" will have an in-game consequence. In many cases, unlike a bow or a sword, it's not even the simulation of a skill. There is no such thing as an ebolt or an energy vortex arising from the waving of a book in the air no matter how ardently I do it.
So what is skill? Situational awareness and effective response to situations. Those are very genuine, very real skills indeed.
Anyone familiar with UO combat mounts will issue the Guard Me command prior to mounting the animal. If someone chooses to dismount you, they've seen you on the mount, they've elected to attack you, they have to know - in advance - that the pet will, in turn, attack them. If they have no counter measure for this clear and obvious inevitability they have, in essence, brought a knife to a gunfight. There is no greater demonstration of the absence of skill, by any definition, than that.