That only goes to show how much stronger he has gotten. Post TS luffy managed to use a gear 3 elephant gatling that was faster then a combined gear 2 and 3 combination that was used by pre TS luffy. Obviously if current luffy were to try that feat he wouldn't have all that extra strain on his body and he would be able to use it a lot better. The same thing happened when he used gear 2 for the first time , he couldn't maintain it for long and it took its toll on luffy , lucci even claimed it was shortening his lifespan. But look at luffy now using gear 2 like nothing.