Exactly, this manga is a parody of romcom, the whole point of parody is to use tropes and clichés and re-contextualize them in a funny way, it doesn't even have to be a subversion, just playing it straight in a context where that doesn't work is enough.I fear that many people aren't seeing the vision.
Yes, a siscon that exists to obstruct a romance is played and usually annoying.
But, in this case, he's a perfect rival and foil for Kimura. A trope-savvy wingman and a super capable anti-wingman engaging in a battle of wits and social maneuvering has so much potential that it could be its own romcom shounen plot.
1, 2, 3, 4. I declare a shipping war!
Granted...Manaka is kinda weak and overflowing with Losing Heroine energy, so this is hardly a fair fight.
Complaining about a parody including a siscon brother or a yandere is like complaining that a shonen parody includes powerups, power of friendship, screaming the names of attacks or even characters screaming their lungs out. If you parody something without using the codes of what you're parodying, is it even a parody?
At the end of the day it comes down to execution, a bad writer can make an excellent idea bad/boring and a good writer can make a bad and tired trope good, and seeing how the manga went thus far, I'd say we have a pretty good one.