A landside lounge is useless.
Having a lounge ‘airside’ before security means having to leave the lounge earlier for your flight, though. But security has never been bad for me at LaGuardia — the different terminals and piers have helped ensure that. And American Express Platinum and Centurion cardholders get Global Entry or PreCheck signup fees rebated. Either gets you PreCheck access if you qualify, and should further reduce wait time.
They’re planning to add a screen showing security wait times near the entry to the lounge, so that will help reassure guests as well.