If The One is limited to his one minute then 4C Mael outlasts him and wins. In the hypothetical scenario that The One could last indefinitely I am not so sure anymore. I always putted The One into the 200K+ range, which is the same as 4C Mael right now. The One has the better feats right now, he oneshotted AM Mel with a credit card swipe (lol), meanwhile 4C Mael's attack was resisted by King and Diane (with the help of Gowther's technique of course, otherwise they'd have been oneshotted too). Dunno, I would say Mael with high to extreme difficulty because of his versatility: he can use PoL and PoD or a combination of them to attack, he can fly and has good regeneration. He should have a high physical strenght, too. He seems way more versatile than The One, who is only a physical power house.
5C Mel vs 4C Mael: Meliodas wins easily for me. Higher base, one more commandment absorbed and better absorption of them. It doesn't make sense to me that a Goddess could absorb 4C and control them in the matter of minutes, meanwhile Mel, who is a demon (and unlike Mael, he is fully compatible with the commandments), would last half a day in absorbing them for only to get the same power increase and techiques that Mael has. It's sounds unfair and makes no sense, IMO. Obviously the "light and darkness won't work on Mael anymore" is just an hyperbole, unless you think that he could easily tank attacks from the DK or the SD with PoD and PoL respectively with no damage. Sariel meant that at the moment there wasn't anyone strong enough for PoD and PoL attacks to work. It doesn't mean that PoD and PoL attacks from stronger people than him won't work at all.