Okay true. The problem of the situation of Marco being with another girl could be resolved two ways;
The extremely deep and proper method; Cope and learn to live with your mistakes, growing from them...
Or the much more common, comfy, suitable for cartoons (and also prevalent in romantic/romantic comedy movies); Fuck that relationship, Main Characters ship fo' days.
I'm still putting money on Starco as endgame, because I don't honestly believes the creators would go for the former.
There is also bias, because I believe Jackie is too undeveloped and too uninteresting (outside of being a load of anon's waifu-bait) to be the endgame. MAYBE if the show had more episodes of her actually being the focus, then I'd lean more towards Jarco being the endgame.
But no. They didn't. So I don't think so.
Actually now that I type that up I just realized; I haven't seen anyone defend Jarco. The best I've seen was when people on /co/ say Starco is garbage and Star's not good.