In the early 70s, those my age considered The Sweet's Little Willy and Fox On The Run "Bubblegum Music." Those songs charted well here nonetheless. Kids loved that stuff.
It was their original version of Fox On The Run that I liked...
Sweet had a running battle with their production/management team (Chinn & Chapman) who insisted in writing their bubblegum hit A sides. The Sweet got their own way with much edgier, rock oriented B sides, but these rarely got airplay. Would have been more to the tastes of more mature, discerning fans like yourself.
But at least you heard of them and acknowledged their popularity, albeit among the teenyboppers.
You mentioned not having heard of Slade until now which always bemuses me. Their hits tended to come straight into the charts at number one here in the UK (the last time that had happened was, you guessed it, The Beatles - with "Get Back") and they generally tended to always pip Sweet to the post here, in a Beatles v Stones sort of way.
More poppy and teenybop lightweight than either Slade or Sweet (or, indeed T.Rex) were The Osmonds who were huge over here around '72ish but only really bothered with by young girl fans (hordes of them though!). Their particular fanbase was eclipsed in 1975 with the tartan-clad Scottish group The Bay City Rollers.
There was a lot of juvenile, flamboyant fun around in the first half of the 70s in the UK (singles) charts and pop scene. Although there was a little bit of overlap, the Americans seemed to go for more introspective, mature stuff like Joni Mitchell, Three Dog Night, Carole King or Simon & Garfunkel etc.
Ironically I always got the feeling that the immediately solo Beatles were more popular Stateside than they were here at home.