Hot take but Shanks might have a better fighting kit than Roger and could end being Roger on steroids

Both Shanks and Roger are some of the strongest Haki of all time. Regardless of who do you think is a superior Haki user, I think anyone can agree that they should be close in Haki as they are basically Hakimans.

However, Shanks could have abilities Roger did not have. First if Observation Killing which seems an ability exclusive to Shanks, plus it wouldn't make sense for Roger to fail to beat Garp/WB if he could kill their FS as he simply would've wrecked them if they couldn't use his FS.

And then you have the fact that Shanks could possibly be in possession of a mythological DF sword which could give him a massive boost in power above Roger who did not have an special sword. Now, I'm aware this is headcanon but it's likely given Shamrock's sword looks exactly the same as Shank's and he has a Cerberus fruit while Shanks couls have the Gryphon sword.

Shanks was also said to be talented enough to use one of Roger's greatest tecniques at a very young age which no one else in the crew could use and that's without Roger training him. Now, if a very young Shanks can do all that imagine what current Shanks can do, he could possibly do any Roger's tecnique and potentially create his own Haki attacks that might excede even Roger's

So to end all this, Shanks is possibly Roger on steroids, insane mastery of Haki just like Roger had but also on top of Observation Killing which is a very OP ability and a DF sword which also would boost his power massively