We can't look at pre-skip Moriah's strength and use it to gauge that he was too weak to face Kaidou.
By the time Thriller Bark rolled around it had been over a decade since Moriah suffered that crushing defeat at the hands of Kaido, it's safe to assume that Kaido could have made some significant gains in those years and Moriah himself has been flat out stated to be far stronger back in his prime. Chapter 0 gives us a peek at a much different Moria who is physically fit and full of ambition hearing Roger's dying words, his words on Thriller Bark paint a picture of himself as an idealistic Luffy type pirate who would recklessly lead his crew from the helm, and Doflamingo laments the huge amount of power he lost from letting himself grow out of shape. To me all of this seems to be building to a return to form for Moriah, he's going to return as the beast Oda has hyped he once was and be a major player in the saga, not Yonkou level, but still a respectable force.
He was specifically stated to be a rival of Kaido who once fought on even footing with him, the entire context of the scene doesn't make sense otherwise. "What!? Moriah, who once fought on par with Kaido, was defeated!!!" that line was clearly thrown in to show what an accomplished pirate Moria was and why beating him was a big deal. Reading it as "Oh… Moriah, who got his ass kicked by Kaido, was defeated." doesn't fit the context at all.
@HacheBe:
Did moriah even directly hit Luffy at any moment? I mean idk how haki works exactly or how it works in conjunction with DF's but i don't think that he can infuse his shadow and the only time he really was getting hit by Luffy was nightmare Luffy and when he did his whole shadow asgard thing. In the first case he was gonna get wrecked no matter what and in the second he was probably concentrating more on holding the shadows in.
He hit him while in Shadow Asgard, though at that point he was highly disoriented, groggy, and mainly trying to maintain his shadow's because he just took a massive beating from Nightmare Luffy and absorbed too many shadows to properly control. It's not impossible that Moria had haki at that point, but there was really no indication of it either. He should certainly have had it back in the day because it's basically a requirement to becoming a notable New World pirate.
@Sang:
As for Moriah, he couldn't have been that equal to Kaido when he lost his whole crew to him.
I don't think that really tells us anything about how the two actually compared to each other. On paper the Baroque Works and CP9 suffered a pretty overwhelming defeat against the Strawhats, they lost every member without taking down a single Strawhat (who could have finished them off if they were more bloodthirsty), yet you can't exactly claim the two organizations weren't comparable and didn't give the Strawhats a hell of a fight regardless. In the case of Moria vs Kaido, we don't even know how much return damage he inflicted, Kaido could have very well lost many members in the battle where he slaughtered Moria's crew. All we really know is that Moria lost the battle and had his crew slaughtered, anything else is just assumptions at this point, people like to write off Moria because he didn't have the most impressive showing, but Oda has built him up as a pretty powerful pirate worthy of respect before tragedy struck him.
He wasn't equal to Kaido in that fight, he was weaker or else he wouldn't have lost, but by what magnitude is unknown. They could have also had several skirmishes prior to that point like Shanks/Mihawk, but Kaido had the higher growth rate and pulled ahead that match. Moriah has been given big ties to Kaido, so I am expecting something to come of that during his arc.
