I was confused on those at first too. They've got a restriction on them so that you can only use them on hero cards (not monster) that are of rank 9 or greater. So using them on an 8 or lower card will not work.
While it's probably good advice to use that stuff on the higher cards for more benefit in general, I wish that I was able to use it on the lower value cards, as it would make flushes that more reliable to achieve with the ability (as you can do with the help of the tactics ability).
I had very little space for abilities in the PICO-8 version (code size limits), so defensive/aggressive stance do double duty, serving as "high-rank cards synergy" as well. It does come off as a bit of a weird restriction, I agree.
The Steam version already has a few more abilities/card types to make high-rank builds more viable.