If you can't tell, I actually think functional tests have a lot more value than most unit tests :)
Kent Dodd agrees with me. [1]
This isn't to say I see no value in unit tests, just that they should tend towards describing the function of the code under test, not the implementation.
[1] https://kentcdodds.com/blog/the-testing-trophy-and-testing-c...
The goal of unit tests is to circumvent problems with performance or specificity from functional tests.
If you haven't seen those problems with yours, unit tests would be useless.