I think he could. Look at the last couple of seasons. Last year him and Hamilton went at it at Canada, with Hamilton being unable to pass him. Granted he probably stopped trying once the penalty was assessed, but he wasn't able to do it before. Seb did a good job of keeping him behind, and if that penalty never happens maybe he doesn't lose his marbles and drive like shit the rest of the year. That coupled with Ferrari's inability to get out of their own way with team orders.
2018 he finished second, even with the metric ton of mistakes he made during the season. 88 points behind Hamilton.
I think in "equal" cars, Seb would put up a real challenge to Hamilton.