The problem this thread makes is that it assumes that Yonko Commanders are far from the Yonko themselves, when this isn't quite the case. At least not in the examples you used.
Looking at Whitebeard against any of the three Admirals, it's obvious the Admirals were on his level and any of them could have beat him one on one. And yes, he was weakened, but there is zero evidence anything but Whitebeard's stamina and natural reaction speeds were affected by his old age. His Quakes, Haki, speed, physical strength, none of it was ever shown or stated to be weaker as a result of his age, and none of those things were an advantage against the Admirals any time he clashed with them except for one instance where he jumped Akainu(meaning, an invalid clash). While WB was the weakest of the Yonko, he was still one of the Yonko.
Oda has never portrayed the Yonko as above the Admirals.
Zero evidence?
Marco comments on his health in the middle of the battle. Says that Squardo shouldn't have been able to attack him, his haki should have been enough to strike Aokiji and that his King Haki was out of action due to his health (might have to check that last one, but I feel I remember it). It was definitely shown that it was more than you're insinuating. He was sick, old and by far not in his prime. Wasn't there a statement from Oda saying something that his quakes were just as destructive as always? Suggesting that the rest of his strengths may have diminished...... I agree his quakes had the same destructive force and arguably his haki (to some extent observation) shouldn't have faltered, but the evidence shows otherwise.
....Granted, not looking perhaps Aokiji was just doing that phasing thing where you're being struck, that was haki doesn't matter and it goes right through you... always thought that scene looked weird.
But here for example,
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.
Which then in turn caused all this to happen,
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He stated here he wasn't able to save Ace, which we have seen Rayleigh specifically target people in a crowd with Kings haki,
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Once again, an admiral isn't effected by his attacks,
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I think it's very questionable that he's shown so little display of haki, even for pre-timeskip. Whitebeard, the worlds strongest man should have used it in multiple occasions and yet he didn't. His health was severely effected and I think you're definitely downplaying his condition, and the effects it had on him.