I haven't seen Dory yet - my wife has and her reaction was kind of like yours.. Its ok, but nowhere near as good as Finding Nemo.. Now, I liked Finding Nemo, which is amazing because traditionally I don't dig animated movies..
So, we saw Secret Life of Pets the day after it opened and we both really enjoyed it.. It wasn't plot-wise, totally what I thought it would be, but I thought it was very nicely done.. Snowball, the cute, yet psychotic bunny, is my new hero..
I think you'd probably like secret Life of Pets.. I get it on the "plot" thing you mentioned in regards to Dory.. While I haven't seen Dory, 2 of the last 4 movies we saw in the last month suffered from poor plots, imo.. Independence Day and The Shallows.. Why go to the trouble of making a movie when you have a poor plot?
Friendship is like peeing your pants.. Everybody can see it, but only you can feel the warmth..