Happy Hogan is pretty much just one of the MCU's whipping boys. Despite the fact that he's tasked with protecting Tony Stark, he's woefully under-qualified (though he's now in a different, more logistical job anyway) and he's barely won a fight since he first turned up. That's sort of his thing though, and being placed in mortal peril to give Stark a reminder of the fragility of those he loves is more his function than being a power player.
In the context of the heroes, he's a bit of a schlub - he can box, thanks to his backstory, but while he has access to Stark technology, he's definitely bottom of the rung, and with a threat as big as Thanos, he probably needs to watch his back more than ever.
Stellan Skarsgard's genius professor was badly let down by Thor: The Dark World's numb-headed attempt to make him a comedy character (while laughing at mental health issues). It turned him from a fearsome intellect valuable enough for Loki to kidnap in The Avengers to a completely undermined fool, even though Thor turned to him again in Age Of Ultron.
He's back for Infinity War, but maybe don't expect him to have any real influence on events: he's probably there to offer some pseudo-scientific explanation of other realms or something. In a straight fight with a giant powerful space alien, he's only slightly more useful than Happy Hogan.