You can never be too strong. Of course you can very easily be too heavy. But this special pull up strength program you are doing will not increase mass at all so that’s no concern. The added weight is a cool party trick (I used to be able to do a couple of pull ups with my 110 pound girl friend hanging on my back). But the really functional part that will come from this type of strength gain will be your increase in local muscular endurance. Navy SEALs that I work with use this program to improve their number of pull ups in a minute which is part of one of their selection tests. They start off quite skeptical that never doing more than 3 or 4 pull ups in a set will actually increase their endurance. But everyone who has every used the program, including these super strong (but muscle heavy) SEALs has seen big gains in the local muscular endurance that allows lots of pull ups.
So this will make you stronger and give you more endurance as well.