Hulk was drained during his fight with Abomination from what they did earlier. If he wasn't the fight with Abomination likely would've ended quicker.
Also if I remember right Thanos didn't even use the Infinity Stone on the Hulk and I don't remember it being stated to enhance him physically. So he pretty much beat down the Hulk extremely quickly.
I do expect Hulk to get stronger in Avengers 4/Another MCU film however