I think this is coming from a very StarCo mindset and I've seen it a few times lingering around. Essentially boils down to, they feel like JarCo actually ever was a challenge to StarCo (which if you look at the underlying writing, it wasn't) and thus feel that because it ended so soon (and we saw so little of it) that it somehow detracts from it and makes it all pointless (and they could be right).

So far, Marco has not really gained anything of lasting value from JarCo, only Star has. If things are left as they are ... then yeah JarCo really was just a cheap stalling tactic to push Star to realize her feelings and was therefore a giant waste of time. However, this assumes that the growth Marco was meant to have from JarCo was merely a boost in confidence ... which I am not so certain it was.

I've talked at length about this before so all I'll say is, take a look at the two "Grand Gestures" (one to Jackie one to Star) that Marco made during 3a and notice the major difference and what that difference likely implies... :D