A five minute cooldown would definitely work, but the balance team aren't keen on that sort of restriction. JLI were brought down specifically so you could mix them into an infantry composition.
I think 3 man is the way to go. They can keep their strong long range performance, but if not properly supported they'll get clubbed hard by CQC and vehicles.
Well I was not thinking that it should start on cooldown like for example osttruppen, but that they should get a 5 minute cooldown after each deployment. That way you could still theoretically get a fair few of them over the course of a game, but their spamming potential would be severely limited, just like their option as panic button (think pre-patch puma, though with a different purpose).