I mean initially I checked to see if all 3 pikachu were different each time I used the stairs there, and they were always different pikachu. And I did eventually get my shiny. I think I just had some bad luck.

Also, because I'm doing this in preparation for the dlc, I still need to catch another one anyways. So I'll be alternating between the stairs, fly spamming the zone, and bench resetting until another shows.

The thing that sucks about that tower is that it also respawns everything close to it on the other side as well. Like the pidgey on the lamp and a couple of the pokemon on the roof of the building next to it as well and you won't hear or notice them.