Saw this on Twitter, and intention is not to target the OP (I like her Tweets), point is to underline something OP has unintentionally highlighted— Shipping vs Misinformation...
OP has, rightly or wrongly, implied pushback against Shisui x MaoMao is homophobic (a part of it maybe true, given the polarisation) and implied that Rikuson x MaoMao will not apparently face the same flak. I don't know that but I think Rikuson x MaoMao also faced criticism, as there are people who shipped them despite there being an ACTUAL age gap of almost 10 years. Multi-shipping is part of fandom, and I have seen plenty of wlw shippers in this fandom (though I am not one). So, to say pushback against Shimao is just gender, it is not true. Suirei x Maomao hardly have any haters. While one can debate gender non-stop, I feel that pushback against Shisui x MaoMao came out of some very important other reasons as well— lot of misinformation and exaggerated anime-only scenes that became the basis of that shipping. Moreover, people were being very hypocritical in contrasting Shisui with Jinshi, so I feel like this kind of pushback was in making for a while now.. It will happen with Rikuson also, if similar level of hypocrisy is shown there as well. The discourse around this ship (and not the ship itself because who cares who ships whom, especially of a character who is not even there long enough in the narrative) has been jarring. Some points of contention include—
Flawed logic: One thing that baffled me in people pushing for Shisui was how eager they were about giving her a pass when Jinshi has been dragged through mud for less harmful things. 'Jinshi trapped MaoMao' crowd conveniently ignores Shisui actually kidnapped MaoMao, became reason for her losing last days with Xiaolan and left her with considerable emotional baggage for a rebelion Maomao had nothing to do with. At least, Jinshi's actions involve some direct or indirect stakes for Maomao, she had nothing to do with whatever was happening in Shi clan. People say Jinshi drags Maomao into palace politics but first person to drag Maomao directly into war involving royalty is Shisui.
'MaoMao felt safe enough with Shisui as a hostage' fan club conveniently forgets why MaoMao wore Jinshi's hairpin throughout her stay because inside her heart she was scared of never being able to return. And MaoMao has hardly reacted emotionally in her first kidnapping, and yes this time of course there was a trust factor, but she also realised she had been dragged here as part of something larger and would be kept alive because of that. It is when the battle actually breaks out, her fears surface more expressively.
Exaggeration: Half of scenes that imply "chemistry" between Shisui and MaoMao were anime-only improvisation, a fact many of people have completely ignored. And fans of this ship not only use these exaggerated, anime-only scenes to spread misinformation about canon, they also tend to exaggerate lack of such fast-pace development in Jinshi's case (where the slow-paced unraveling is actually the whole point). I liked this post on Tumblr that goes like people are so habitual of subverting canon in the name of headcanon/fanon, that when people actually enjoy canon and storyline as it is, they tend to fault it in ridiculous ways.
Love as a budding feeling: I have a personal problem with misinformation spread around this ship and slightly unwanted elevation of Shisui at par with protagonists and 'implied' chemistry takes because the author has left no scope for a third person entry in JinMao dynamic (so far). One of the fundamental aspects of Jinshi and MaoMao is the fact that they both are experiencing such feelings for the first time. This is an important subtext to maintain if one has to gauge their relationship fully. So, it would do creatives good if such improvisations of a character's importance are avoided, be it Rikuson or Shisui (though they have remained faithful to the source material). I mean if the anime will project Rikuson something of a love rival, it would not be fine. That is why also those small scenes like hairpin and balcony ones anime dropped were important, and why those scenes of unnecessary touches and prolonging Shisui's end was exaggeration and not required. These subtleties matter in a relationship like JinMao. The thing that sets apart Jinshi x MaoMao is that their relationship has no past or third-person baggage, that is why it feels so domestic and normal. I feel like manga version stayed more loyal to the source material in this arc.
Actions Speak Louder Than Words— er, Selectively: It is amusing to me that people use MaoMao's annoyance with Jinshi to discredit his years-worth of progress and development in their relationship while they see small signs in comparatively just an year-long relationship as proof of love between two. So, pull-and-push dynamic and scenes between Jinshi and MaoMao should be discredited because apparently she is annoyed with him or doesn't show any grand emotion to him despite doing things for him she would do only for Loumen but emotional state of MaoMao amid the crisis of war and realisation of a friend walking towards her death is a sign of romantic love? In one case, MaoMao's emotional constitution is not clear in her actions, in another it is? My friend, what?
LET WOMEN HAVE DEEP (AND EMOTIONALLY CHARGED) FRIENDSHIPS/RELATIONSHIPS WITH OTHER WOMEN WITHOUT MAKING IT ROMANTIC OR SEXUAL: What happened to women-women friendships with baggage? With tragedy? With hurt and pain? What happened to complicated women-women relationships? What happened to meaningful women-women relationships? What happened to nuances?
Thus this pushback is necessary especially when romance is such a carefully crafted nuance in the story. I feel like it has tried to prevent itself from becoming exactly what these people want it to become— a character with multiple love interests. This is very important for MaoMao as one of her basic characteristics is that her cold demeanor and deadpan practicality prevents people from seeing her as a romantic partner, so much so, even Jinshi is temporarily frustrated after a point. MaoMao's non-romantic associations are indispensable to her growth with Jinshi because it is Jinshi's persistence and pursuit that finally alters MaoMao's idea of belonging (and that too not completely). To try to impose that she felt this in a relationship which barely lasted a year and ended with an emotional upheaval in her life is pretty insulting to whatever author has tried to showcase in this dynamic.
Otherwise, shipping has happened between Lihua x Gyoukyou, so I don't think gender is the only problem here. For once, people have found a story as organic as TAD which leaves little room for implied dynamics given how nuanced and slow-paced all canon dynamics are. You get answer to almost everything Maomao and Jinshi do wrt each other, and there is actually very little room for misinterpretation. Justifying misinformation or hating on canon unreasonably is certainly odd for a story like TAD that leaves little to misinterpretation. Therefore, some aggressive pushback is important against these 'ships'. Not all of us need subversion of perfectly intelligent writing, romance or storyline.... Also, gives the appropriate message that author was right in what she wrote and plenty of people enjoy the canon as it is...