I tend to think that for a lot of people "it's boring" is their code for "I don't like it". But that's just my personal theory.
I tend to think that even aside from whether Marbecca is cute, it's not a boring story. I have a huge problem with VL right now that it's very... toothless. Like the show is always afraid for anybody to do anything truly controversial. Especially in the Tanja vs. Clarissa story. Rather than letting people do something truly bad and then letting them deal with it realistically, it's like the show always pacifies and backpaddles and sugarcoats.
Like there is a big war about Clarissa vs. Tanja among the fans and whether the show is painting Tanja to favorably. And to me, while I do think that it's somewhat questionable that they kind of paint Tanja as "the good one" now, I think what makes it even worse is that they don't make Clarissa the truly bad one either. They always stop short of anything actually interesting happening (Seb actually sleeping with Sonja, Tanja actually pushing Sonja during a quarrel, Clarissa actually setting this up intentional,
Don't get me wrong, at other periods of the show the show actually overdid it with letting the characters do questionable and even nasty things, but to me it's too much in the other direction now.
I retrospect, I almost prefer the previous year of the show, there the pacing was slow, but the topics were actually serious and they came to a logical dramatic peak.
- Good girl Helena running over the show's resident main hero with her car and killing him
- Ansgar almost sleeping with his daughter/Victoria rushing into the hotel room and preventing the incest in the last second
- Twins Jan and Julia actually getting their happy end
Now it seems like VL always weasels out before the big logical climax for a lot of stories, especially Clarissa vs. Tanja and only brings the softened up version. I like Marbecca too because it's the only story that actually feels like there's something real on the table, where the chance that people might lose something feels real and not like "Bah, no matter, the show will just find a way to soften the blow so much it will become insignificant".
So even though I think there are parts that could be written better/with even more tension (like if they included more of the rest of the family), I think overall it's a good story. Especially since I feel the show has enough nice and non-threatening stories anyway (for example with the teen couples).
I get people's complaint that it's slow moving, but honestly, it's not a complaint I can particularly agree with. I think it's really just the current slow attention span of people. IMO VL is already too fast moving in a lot of areas, like a lot of stuff happing in the span of a few weeks and then suddenly not mattering anymore. I think soap stories have to be slow moving and I think this is also why Marbecca appeals to me. It's a very traditional story in that way. And again, I don't feel like it really slows down the show itself because to me everything around it is still (in part even too) fast moving.
Plus to me there are too many examples recently on the show where couples did get together very quickly and suddenly all the tension and appeal is gone. For example Kim and Emilio who entered into a teenage marriage. They now have some occasionally entertaining mini plots, but it doesn't really feel like a love story anymore. The same for Jessica and Daniel.
So yeah, I'd rather have some really old fashioned love story like Marbecca even if the cost is that it takes a long time. Better that than to get together quickly and be over the next day. It's kinda selfish, but if they're going to do a lesbian story, I'd rather it be a big one. Especially since VL doesn't really 'do' easy feel good stories/is really, really, really bad at them when they try.
As for Rebecca not caring about Tristan that much. I get why it's bad, but I also get why it is that way. There was a really, really cool line in the Hagen/Dana story which dealt with the fact how much it would mean for Dana to betray Marlene and why that would be so bad for the family. Hagen basically said that Marlene's family is a real family while the Lahnstein family is really just a accumulation of individualists, where everybody is pretty much doing their own thing. So I get why Tristan is more like an abstract duty to Rebecca rather than a real emotional connection, especially since they've usually been portrayed as the opposite of close in all their previous stories but at the most occasional allies. (and I rather like the the show is keeping it that way, that it's more "how can you be of use to me/how can we find some joined use" rather than "I really like you")
It's one of the few things I wish the story would mine more, to shine some contrast on that. Just how different Dana/Marlene is to Tristan/Rebecca. And that what Rebecca would be breaking if she got together with Marlene would be very different than what Dana broke when she got with Hagen. Or just explore Marlene's feelings about what it means to her to suddenly be the position that Hagen and Dana put her in last year.