#2 Rusev
Rusev came to the WWE as an unknown entity, but he quickly rose through the ranks in NXT, and made his main roster debut as an incredibly hot prospect. The Super Athlete quickly tore through the main roster, going on a massive winning streak, but as we've seen plenty of times, he fell to two different WWE cliches: Super Cena and the foreign heel trope.
When a foreign heel comes to the main roster, they often go on a big undefeated streak, lose a big match and then descend into comedy/undercard status, and despite all his potential, it happened to The Super Athlete too.
Unlike others, Rusev managed to overcome that demotion, and he coined the 'Rusev Day' moniker that's made him incredibly popular with the WWE Universe, but unfortunately, WWE just have no interest in pushing him, and again have missed out on the chance to make a new, fresh main event star.