I don't what is Your opinion on harbor as agent but I think he is super weak compared to viper on maps like Fracture, Breeze and Icebox. So here are some buff that I think are adequate in order to be good controller agent :-
C ability :- According to C ability is good and bad at the same time. If devs increase the slow from that wall or add a Nearsighted blind to that ability it would be good also It should last 10 secs
Q ability:- The shield is so fragile, Imagine you use it to retake a sight and defuse spike enemy team will just spam and break that in no time. So potential buff for that ability is that they increase either the durability of that shield and also even if the shield gets broken the smoke should last for 12-15 sec and it should be a rechargeable ability like astra. 40 sec Cooldown would be nice
E Ability :- Harbors wall is Only that one ability that I find find good but the cooldown is massive (40 sec) . Viper can use her wall twice in that time so I think devs should reduce the cooldown of that wall and may be increasing its length a little bit
Ultimate Ability :- His ultimate is good for getting site control but the stuns take some much time to stun the enemy so may be reducing that stud Animation duration.