I hadn't found something like this for Tears of the Kingdom yet, so I decided to just make one.
If you're just after max stats, then it ultimately doesn't matter which wild horse you catch since you can just RAISE all stats to lv.5 by giving meals to the Horse God Malanya. Even the worst possible stats can be made perfect that way.
The only exceptions are the Giant Horses and Epona, which can't be upgraded - those stats stay the same forever.
However, it might still be beneficial to know which stats you can expect in different herds, because some of them are already pretty close to max right from the start (like for example the Wild 5245 in Group 08) which significantly cuts down the total upgrade cost since those meals can have some rare-ish, expensive ingredienst that are annoying to farm.
(my personal motivation for this however was that I dislike having too many icons on the screen and find horses with just 2 spurs perfect, but all online guides simply point out where the high stats and special horses are and flat-out ignore everything else)
The map does not show the locations of the special horses to avoid spoilers. If you want to find out where the Royal White Stallion, the Giant Horses, Spot or the Golden Horse are, you can find dozens of guides easily =P
Some more extra info:
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The group numbers are taken from the game code and correspond to the "WildHorseCreateTag" sections. WildHorseCreateTag04 and 07 exist but do not seem to have actual map placements, so there is nowhere for them to spawn.
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Some groups have "impossible" stat horses in the game data (like having a zero in a certain stat) but those horses do not seem to actually spawn for some reason. If anyone ever finds a regular horse that has a zero in any stat (except for the Giants and Epona which have zero Pull) please let me know, because as far as I can tell, you can not get Strength below 1 point or any other stat below 2 points. I have no idea why those stat combinations are still in the game code tho.
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One of these "impossible" horses is the "Default" horse, which had a unique coloration in BotW (brown body, white hoof tufts, dark muzzle and very dark hooves) and unique stats (4-3-3-0) but it does not spawn in the wild anymore in TotK. If you import an actual Default Horse from a BotW save file to TotK, it will turn into the "fake" variant (bright hooves, not unique) and get slightly different stats (4-3-3-3) instead.
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Spotted horses only appear after you finished the "Spotting Spot" quest, which in turn requires two completed temples.
For all other horse-related questions, consult HylianAngel's Horse Guide which is for Breath of the Wild, but still has accurate information for the most part since the devs didn't change much between this game and the sequel. Color combinations, temperament and the like are still the same.
If you have additonal information, questions or you spot a mistake, please let me know. If you post this elsewhere, please give proper credit and link back here, thanks.
Hear, hear. I love the horses in these games so much that I can't fathom completing a full playthrough without owning at least one, but it is kinda hard to still find them useful and convenient when there is a free pile of Zonai stuff lying around behind every corner and Autobuild exists. Plus all the restrictions ... the desert? Off limits. The Depths? Off limits. The Sky islands? Off limits. The sea? ...you get the idea. The areas where horses are even allowed to be are already rare, and on top of that you have dozens of chasms, blockades, "Monster Forces" blocking roads, uneven terrain, rivers, lakes, tunnels, caves, wells, mountains that are almost impossible to cross without leaving your horse behind. Trying to find a rideable path around all of that becomes annoying pretty fast.
Personally, I think it was a very bad call to remove the Ancient Saddle & Bridle. Most people were already struggling to keep an interest in horses in BotW because even WITH the saddle it was a hassle to get your four-legged buddy back to your side after you had to glide somewhere, but now that TotK is three times as vast and has a LOT more vertical travel - where the teleportation feature would really shine - they nuke the ONLY way to summon your furry means of transport to your side whenever you want? C'mon, guys. Seriously.
Even if they wanted to get rid of all "ancient tech" then why not let Purah build a substitute? Or put a hidden secret Zonai saddle somehwere? Or make it an amiibo drop? DLC content? Let Robbie invent a special Travel Medallion specifically for horses? Or make Malanya reward the player with a magic flute or whatever?! It really isn't hard to come up with an in-game, in-universe, lore-fitting reason for why a horse teleportation feature can exist.
Or just hide a special saddle with mechanical wings behind some late-game quest to make your horse able to glide.
Likewise. I get wanting to push the devices as transportation but as you said there's enough terrain that requires it already (if you want to navigate other than by foot, rune, or paraglider).
I do feel that there's enough "missing" from the game to indirectly support the idea that DLC was supposed to be a thing. There's enough ancient tech in the game (towers/mapping, fast travel, Purah Pad) that adding another piece wouldn't be out of place.
...now that is one hell of an idea.