People not get that Teach overall states without even his devilfruits are very high, he has also strong haki, I wouldn't be surprise if he has adv CoC too.
The point is that Teach without Df, could scar Shanks and give him his worst scar which Shanks ever got, to a point that not even his scars against Mihawk are on that lvl what Teach give him, a devilfruitless Teach, that alone put Teach as enemy higher than Mihawk for Shanks.
And the same Teach pose now 2 devilfruits, perhaps even 3. He defeat a 3Billion guy pretty much without much issue and im sure he didn't even used awakening...
Teach is dangerous and the strongest character, forget Shanks,Mihawk,Akianu or Dragon, no one will top Teach.
I noticed how Oda always cut in the moment when Teach is about to fight serious:
Ace vs Teach>start with Ace hit him twice, but than Teach fight serious and almost two shot him, fight continue and Teach fights more serious>offpanel>back to fight, Ace is lying down and barely can move while Teach is laughing and the winner one.
Law vs Teach>start also with Law hit Teach and Teach start to fight serious>offpanel>back to fight, Law already defeated lying down, worse shape, in sign of his death, Laughing Teach again as winner.
Oda cut always in the moment when Teach start to fight serious. And short time pass and his opponents lying in front of him, defeated/brutal beaten down.
Teach is probably the most dangerous fighter, haki, his overall states, his dangerous devilfruits, no one can beat him.
For sure the current number one.