Because Oda has also made it abundantly clear for decades that Whitebeard was the only man who was as strong as Roger.
Roger and Whitebeard draw with each other, both extreme diff Garp. Nothing in this chapter changes that. Oda just wants them both to look good.
I can throw a scan of Whitebeard and Oden being equally matched in a clash, it doesn’t make them equals either.