That is a claim, not really telling me the why.

I could argue that by adding these tests, we are not testing integration ones as much as we should.

Additionally, I find that when we need to use mocks, it is a smell that something smaller should be broken out so it can be tested individually. It is bad practice to test private methods as they can change at a whim and would require double maintenance (code and tests) when they were not necessary in the first place.