You clearly don't watch pro games if you think that's the case
Harbor has a shit win rate precisely bc it requires a viper and good coordination to be good, sth ranked will never have
Harbor can also be shit in pro play simply because either teams don't understand harbor viper or they have players like zeek who have 0 idea how to do even half decent walls
Giants for example have 0 fucking idea how to play harbor on pearl. They rarely went b and planted in the shittiest place and used cove like a smoke(which is supposed to be used like a sage wall).
And stalling? Dude are you fucking kidding me, Omen flash doesn't stall well, and it is one of the best stall util on maps like Icebox where you just stack harbor+viper walls for infinite delay.
TMV has a really good video on why harbor viper has 35% win rate.
Plus every controller has some gimmick, and not ever controller needs stalling util(like sage as a sentinel doesn't have a trip but still is picked)
And your argument makes no sense either: you say he has no offense. Even if that is correct(which it def isn't with a strong ult and 2 walls), you proceeded to say that it's shit at defense(which you think is "offensive ability" for some reason.
Harbor is perfectly balanced, and any buffs will litearly break him as an agent.