Play the fight as Leo even on hard and jack is piss easy. The other way around is a nightmare.
"you think that tree whacker can match bps tech? gimme a fuckin break"
truer words never spoken. anyway I'll help you. There should be a Tyre / buoy to throw at Leo. throw it at him. Hit him with LT+Y. pick up tyre. throw again. repeat. you win.
If he gives you shit when trying to throw it grab his ass. Jack is a get close grab and chainsaw type of guy.