@Ubiq:
Shanks' conversation with Whitebeard seems to suggest that Teach was already as strong as he was back when he had both arms and Teach didn't have a Logia.
So unless Shanks has somehow managed to become vastly stronger after losing his arm (which seems doubtful judging by Mihawk's lack of interest in him as a potential opponent), Teach is now welll ahead of him in strength. Even a weakling would become a powerhouse with a Logia and Teach was no weakling.
Shanks conversation seemed to be a concern for Ace's safety more than anything.
Shanks at this moment in One Piece is vastly stronger than he was back then. Losing an arm won't hinder his skills, BTW Shanks at this moment is going head up with the STRONGEST man in the world with that one arm…..Teach (Blackbeard) is NOT on Shanks level.
@Polygon:
BB gave him a scar, there's not even a mention of an actual fight. I seriously doubt BB is sstronger than, or even on the same level, as Ace without his logia fruit. Also, NO ONE is gong to be well-ahead of shanks in strengh, no one. There is only one known person so far who is stronger than shanks, and that is WB. And even that is not a big differance.
What? Blackbeard GIVING shanks that scar is showing you that Blackbeard is one powerful @#%*! in some way you can say that he is on Shanks level. To say that "NOONE" is equal to Shanks strength wise is ridiculous…their are tons of monsters and Hawkeyes is stronger or equal to Shanks!!!!!