Not gonna compare Koichi and Midoriya. They are both likable imo (though I prefer Deku). Koichi was an odd duck in ways different than Deku. The fact that he considered marrying Makoto (whom he hardly seemed enamored with) was just strange. Yeah, Knuckle Duster was a cool, crusty mentor but for me he was no All Might.
What I did not enjoy about Vigilantes was the sometimes stupid arcs (Captain Celebrity annoyed me so much that I dropped the title for quite awhile), the simplified style (a lot of the characters look like some sort of lizard, including the pre-nomu things that were explosive) and most of all, the inconsistencies that didn't jibe with MHA:
The prototype nomu were acceptable, but then we have Hood--already shown as a nomu when we see him still in the Doctor's processing tubes in the main title. On top of that we have Kurogiri and super duper villain Six, notably advanced nomu (far advanced over the first ones seen in MHA and even the 'High Ends' of which Hood is a member). Why bother showing the gradual evolution of nomu in MHA when we have superior examples already having been made?
Stuffing character origins into Vigilantes' plot were just out of place (Stain's backstory and how he lost his nose never even made it to MHA at all). The entire Shirakumo story appearing in Vigilantes left MHA flatfooted since little of Aizawa and Mic's past was alluded to until the Kurogiri reveal. Speaking of which, switching a very different character such as Kurogiri into a specialized nomu based on Shirakumo just didn't fly that well for me.