He's more like Elton John than Wham.
i don't really like either of those comparisons. i mean, elton john is one of the most accomplished singer-songwriters of all time. his success was multi-generational; his longevity was brodeur-like. wham! had five enormous hits any one of us can hum the chorus of on a moment's notice, and one member of that group went on to become a huge solo star... idk, like how jean ratelle had his run with the GAG line, then had that second career where he left rod gilbert behind and didn't suck in the playoffs with boston.
if we're talking about two hit wonders, that's an artist or band who only had two memorable songs. sometimes that's a band that had a brief period of success, fell off that form and were unable to get it back, and then broke up/retired/disappeared; musical example would be arrested development.
in 1992 they put out an album with two smash hits. by '94, they were gone.
of guys previously mentioned, jim carey is a good comparison here. big rookie year, vezina sophomore year, then stumbled until he quickly gave up.
then there's the artist/band that has two big hits, and plugs away for a decent amount of time. maybe a minor hit here or there that if i played it for you you'd kind of remember it but in the end all anyone really knows are those two songs.
i don't know how you don't consider tim thomas in this category. it doesn't mean he was literally out of the league, or literally a backup when he wasn't "hitting." it just means he was average otherwise. for instance, google coolio's song "too hot," or "c u when you get there." those songs played on the radio; but no one is playing them on the old school lunch hour in 2017. bill ranford is another name for this category.
and then you have the kind of two hit wonder that has a long, respectable career. a lot of staying power, and have a good loyal following, their fans would yell at you for an hour for even suggesting that they were two hit wonders. but everything is eclipsed by two transcendent moments. there are other seal songs, and some of them are fantastic songs, but even your mom knows "crazy" and "kiss from a rose."
i mean, you could even call the sedins two hit wonders and i wouldn't argue. they had a lot of point/game seasons, all-star seasons, fringe top ten/twenty seasons, but for two years they were true MVP-level superstars.
but anyway, i think all of those "kinds" of two-hit wonders are still valid.