@sgamer82:
It's important to note that Shoto does not have two quirks. He has a single quirk, "Half-Hot Half-Cold", which is a down the middle combination of his parents' quirks. He's never been regarded as having two quirks in story.
@desa:
Quirks are supposed to be a combination.I&F ended up with the combination that the father deemed perfect but they are not not 2 independent quirk.
Ok, then where it reads "two quirks" read a "combo quirk" or "half-half quirk" then.
@Cyclone_Baroness:
Bakugou is technically a perfect mix of his parent's Quirks.
I feel like people did treat Shoto like he was special. But maybe it's because while he's operating two different elements, it's not two wildly different Quirks. They both pretty much function the same.
But yes it is a bit odd to not see more with 2 quirks. But I don't think we'd get something majorly drastic like a flying quirk and plant control. Even the kids at the provisional license test had more unusual Quirks didn't have what looked to be multiple. They were just more refined and out there.
I think it could work if Endeavor and Mother (?) quirks had a similar root. Like Endeavor being able to heat things to such a point it could set them aflame and Mother being able to cool things to such a point it could freeze them. Then trying to get a child that could control temperature to the full range between both extremes would pass as getting two quirks of similar origin to create a more powerful one.
But generating and controlling fire really has nothing to do with being able to create massive amounts of ice, so it feels like two completely unrelated abilities except for the fact both are usually treated as related in fiction (related as being antagonistic). But… yeah, maybe what Horikoshi tried was to use that "usually perceived similarity" so we should see Shoto's quirk as two opposite uses of a same root ability and the reason we don't see more of those is because the parents quirks need to be "compatible" to be able to be combined (and even then, with a small rate of success).