The Difference of Shipping in the Umamusume Fan Content I've observed so far, in a descending list of how in-character the Umas are
UmaxUma (A Rank)
Relatively faithful to the characters' personality and characterizations, though often make use of their character traits exaggerated for comedy.
UmaxFemale!Trainer (A Rank)
Quite faithful, usually with the uma girls being the dominant type though there are some exceptions. The female trainers are also usually have some personalities of their own if not a more defined features.
A specific rarity are uma!trainerxuma yuri, but Uma Trainer alone are already uncommon, and yuri of them even more so.
Female!TrainerxOther characters is quite rare as well, but would be interesting to see.
Special Mention: toji (y2toj2) and their fem!trainer OC, Shirohashi Akari, paired up with Sirius Symboli. They're cute together
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UmaxMale!Trainer (F Rank)
The times when the character retain their personality in the ship is an exception to the rule, and it worked in spite of the norm.
The norm being "the girl is horny for her male trainer, is violently jealous, and incredibly possessive". Sometimes you get the added "bonus" (derogatory) of "she's concerned she doesn't look 'feminine' in front of Trainer-san", which is just insulting.
These are Mayano Top Gun's personality, stripped of context and nuances, and done worse. The male trainers are often either the anime trainer, or just a blob with a T for a head/face.
Insert "haha Tracen Academy is setup so Uma Girls can breed with Male Trainers to ensure future Uma Generations" joke here, my beloathed. The Shinzo Abe joke outlived the man himself somehow.
I'd mention the slightly better Male!TrainerxOther Character pairing, but its usually only done in relation to "hehehe she's jealous her 'man' is being 'stolen' by other woman"
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Fucking Umawife "Agenda" (G- Rank)
A domestic Housewife who stays at home with a beautiful daughter, welcoming her beloved dear husband home who had just came back from work. If she has a personality, she's endearingly clingy, or yandere-ish jealous, but in an endearing way of course.
That's it, that's the exact template for this cookie cutter slop.
Who the girl in question doesn't matter, it's the exact same. Maybe you get some lip service on who they are MAYBE, but its just the same junk with replaceable heads. Insert Umawife agenda comments, my beloathed.
Conclusion
I hate Male!TrainerxUma and Umawife content because they're boring slops, even the common ones did not do justice to the character they're 'inspired' by. It's all the same 'joke' and every artist who made it think they're breaking new grounds instead of treading the same old road.
If the artists wants to make those arts, more power to them, but good grief I do not enjoy seeing the subreddit translates overwhelmingly the same sort of content instead of something with some modicum of interesting material.
Bottomline: I'd take an interesting slop over boring tired slopfest, the bar is on the ground with "have the uma girl stay in character" and a lot dug under it instead.