the thing is that if you want to watch the show and perceive sherlock/john as platonic, you have to watch the entire show set on a platonic level, you don’t choose what should be platonic or romantic when something doesn’t suit your tastes or makes you uncomfortable.
john “moving on” from one relationship (his best friend) to another (his future wife) doesn’t make sense on a platonic level. and i know that some people do have very deep and meaningful friendships in their lives, so much that if their best friends would have to die (or worse, to kill themself) they would be desperate, grieving for years and years and i do get that and i respect that and i do think that friendship can be and is as important as romantic love, seriously.
but in the context of this show, john moving from a platonic relationship to a romantic relationship and saying almost textually in TEH that is for him the same thing doesn’t make sense. you don’t, even if you love deeply your best friend in a platonic way, decide to move on from this friendship to a romantic relationship, especially if your love interest is not introduced as “oh she’s also his best friend!” (it could have worked if the creators had wanted to keep the “no homo” as strong as before).
it would have made sense if john had said to mrs hudson: “i’m very close to this woman, she’s such a good friend, i moved on and i found a new best friend” but no, he said: “i’m moving on (from sherlock’s death) and by doing so i’m going to marry a woman because my feelings for sherlock are equal to the feelings i have for mary”
this whole conversation makes only sense if you interpret john’s feelings towards sherlock as romantic. the whole “platonic soulmates” thing does work in a way but you do have to explain a few things later on.
also don’t get me started on the awful proposal where john basically said: “yeah mary meeting you was the best thing that could have happened to me because you know you’re second best and i don’t have any other option and i’m so lonely and i want to be in a romantic relationship with someone who’s alive and needs me and loves me because my best friend who died didn’t return my feelings and i loved him so much so here have a ring do you want more wine?”
YEP.
(That really was a terrible proposal. Although admittedly I didn’t think it was quite as bad as this makes it sound.)