The downside is that you’re using assets in the context of cap space to not fortify a weakness on the team, team defensive play, but using it on an unknown asset in Kane who MIGHT BE a shell of his former self while your team is competent in offense.
It’s like you have a leaky roof on your house that you should fix asap, but you decide to buy a classic car without an engine, to go with your other 4 classic cars beforehand.
It’s just a dumb decision at this time to go after Kane, you don’t need him.