I think making modes for sexuality is a bit much as it would lock the player into a certain role with no way out at the very beginning of the game when they can choose not to advance in the relationship simply by not giving them the bouquet. As for heart level consistency, I think 8 heart for marriage candidates is about the same as 10 hearts for non-marriage candidates. For instance, Emily has 6 heart events and Alex has 5 before you have to give them the bouquet to move on to their 9th heart event (and that's not mentioning all the non-cutscene questions they could ask you). On the other hand, Gus has 4 heart events (2 of which are just getting recipes in the mail from him) and Pam has 3 heart events (two of them just being more recipes and the third having to do with having robin build a certain end game thing before you can even see it). And neither of them asks non-cutscene questions like the marriage candidates do. Even if I decided that I didn't want to romance anyone and got everyone to their max hearts as is, I would feel closer to the marriage candidates as friends then to non-marriage candidates. Because the marriage candidates kinda go through a whole character arc while non-marriage candidates really don't.
And I feel like that really is even. Even if they don't come up to us on their own and say "hey I'm attracted to you" gameplay-wise they show this by how often they interact with us in and out of cutscenes. All the marriage candidates (at the time of writing this at least so who knows if a future update could come along and bite my butt) are young and not settled down yet, that they could be looking for love and have the time and energy to look. Meanwhile, for instance, Gus runs a tavern full time and seems like he always has his hands full and while he appreciates the farmer's friendship, he doesn't seem interested in pursuing anything more than friendship. Pam meanwhile is despondent and at one point tells you "you're good looking, why are you wasting your time on me?" in casual talk, so she's clearly not thinking about romancing you, but can be persuaded into friendship. And I think that's the crux of the matter, all relationships aren't equal in this game but that's kinda how it is in life.
If you're really hoping to make the relationships with everyone feel equal at all heart levels then I think you would need to add more to the non-marriage candidates.
Now since you mentioned getting the whole story, yeah the 8 heart event is where the last of the marriage candidates story is given and the tenth heart event is a romance option. You're not really missing out on any story beats by not getting everyone's 10th heart. You also can get everyone's 10th heart because 8-10 is dating and while you'll have to hurt people to get all of the 10 hearts, you can do it before settling down (you can also do it for those after marriage hearts to but fixing the mess you'll cause with that is a lot more of a hassle/guilt-filled). Hell, there's even a special cutscene for getting everyone's 10th heart at the same time, not that it's great for your farmer. And if ConcernedApe ever wanted to add more fun cutscenes for the marriage candidates pre-dating or marriage, there's no reason he couldn't add them in at 8 hearts or below. The part of me that wants order and structure does agree, friendships for everyone should cap out at 10 hearts, but I really don't think it needs to complicate the romance system in the way you're suggesting to achieve it.
Anyways sorry for the overly long post, especially if it's rambly, it's kinda late here.
Wow, it's been so long since i played that i forgot you had to bouquet some people before they started treating you completely awkwardly, but still, and maybe this a lifestyle difference coming out, but looking back on the wiki to look at Emily in particular, if this were the real world, I'd be having a long talk with her after the
8 heart event, saying
"I'm sorry if you got any ideas, but I'm not interested in you." After that, I would've had a conversation with
clint, informing
him that he probably got the wrong picture from the whole event. With
Haley I would have a similar conversation after
the 6 heart event. Of course, I could stop at these points, but then going in blind, I would assume that i'd know more about these characters and know them much better by continuing anyway.
Then again, we're talking about a game where you give "just friends" valuable items to make them like you more rather than helping them with tasks, because, let's be real here, that's what what we do with everyone in this game. I would probably go out of my way to help
Haley find the bracelet, but not bake her 2 cakes per week or give hear valuable pearls or something like that in real life, so the fact that we're already giving this fairly odd behavior a pass in the first place...
Though, i do agree, overall the characters could use more story. Stardew Valley's story coming almost entirely from character interactions and seeing into their past and learning everyone's vices, makes stardew valley seem relatively short. Outside of that story element, i'm merely growing crops for money and achievements that ultimately for reasons i don't understand. Stardew Valley is more or less the opposite of NetHack, in almost every way, despite seemingly taking some degree of inspiration from it.
And no need for an apology for a long post: the more detailed, the better. That's how discussions work and how free speech solves problems.