Kinds of

This sentence is grammatically incorrect.
The correct sentence for a single breed of dog would be, "This kind of dog is very aggressive."



If you want to write an overly generalized sentence depicting the entire species of dogs as being aggressive, then you might write, "Dogs tend to be very aggressive."

The first is not wrong, and your guess is an accurate one. I think your essential concern is about countable vs. uncountable nouns. Countable nouns can be singular or plural; uncountable nouns are singular. Some words can be both, in different meanings.

Dog used as an uncountable noun means the canine genre - as you say, the species, whereas when used as a countable noun refers to actual dogs or subgroups of the genre.