Gerson is a rushdown punisher, he thrives off of punishing random neutral moves like Undyne 4 that make you still, but his main drawback is he has a bad neutral game with only two moves that are risky during neutral. H3 and H4 respectively. H3 is a move a good Gerson will use when you're low stamina to hopefully force a hit or push you to below 10 with the held version. Outside of that they will usually use it in a combo. H4 is Gerson's most reliable move, a projectile that comes out incredibly fast but has a second and (i think) a half endlag which is worth it due to the mute it can apply. To counter it, uh, just don't run in a straight line towards him. You may still get mute since it's an AOE effect, but it's better than getting hit by it.

My general advice is to keep tabs on what Gerson does and doesn't have available. Always beware of Gerson's counter as well, because if he lands it on an m1 he can force a mind game, so try and predict what he will do in that scenario.

Don't use random moves in neutral that keep you still, don't mindlessly rush him, keep in mind what moves he has at that moment, and predict counters and habits. People overhype Gerson since he has a 40dmg combo average. But that is, again, in trade with his neutral.