The Undertaker was in his prime back then, Kane taking a loss didn't hurt simply because Kane was booked as a machine, he was tearing apart anyone in his path, he still looked unstoppable in defeat as it took 3 Tombstones and he still got up after the match and Tombstoned Taker. The booking comity back then was different as well, they invested in characters, nowadays lazy booking and silly booking like the Wyatt/Cena feud made Bray look quite weak, then he was lost for months.
If Kane debuted now, his booking would be a lot different, he'd be the big monster dominate for a while, job out to a top star and be thrown to the side. The problem is WWE don't invest time and effort in to more than a couple of guys anymore, look at the Midcard, the ridiculous IC Title storyline, repeat matches on TV every week, Missed opportunities e.g. Rowan vs Harper on free TV with no build up.
Bray Wyatt is a man that still hasn't been "Made" yet, I love The Undertaker but Wyatt should go over him at Mania. Also back to Kane, he had a good year in 98, he was kept relevant, Wyatt after his match last year had nothing, he was put in a pointless feud with Jericho, no one cared for it, WWE wasn't putting effort in to rebuilding Bray until the year was closing, even then you could say some of the outcomes of his matches were questionable, he went into a feud with Ambrose who had lost steam never getting his win over Rollins.
WWE Booking in 1998 and WWE booking in 2015 is not comparable.