It's Monkey D. Dragon really... It's all just because of a single phrase; "Most Wanted", which doesn't necessarily mean "Strongest".
But it's happening, people tend to compare him with Roger and Edward when he can most probably be just as strong as an Admiral and his fame come from his Anti-WG ideals, afterall bounty represents threat to WG not the strength of individual...
Others who can't be listed down as over-hyped,
- WB(not fit) fought on equal grounds against Admirals and one of his attacks did destroyed whole Navy HQ...
- Shanks had a little clash with WB and his involvement in the MF made even a rampant Akainu hesitant if he should continue...
- Mihawk, after the whole war, left MF totally unscathed and didn't show any hesitation to go against WB...
- etc...