I'm aware of its significance, but the logical mistake is to believe that 'leader' is meant as an empty statement. It refers to supreme leader, this is why it was translated to conqueror. That's different than just being a simple leader. Supreme Leader / King implies being capable to achieve something of exceptionally and extensively good. You are not a Supreme Leader if you simply possess leadership, the matter points toward something well beyond and deeper than that. This is why Sanji will never be like Ace or Whitebeard.
You’re talking about discovering an entire sea that is said to not exist as not achieving anything exceptional? No man has done it before not even Roger.
And when Ace activated his haki did he think about his ambition or protecting those precious to him.
For every Doflamingo who wanted power to cause suffering and desired to rule there’s an ace who wanted power to protect the friends behind him.
You can’t tell me 9 year old Ace had the aspirations to rule the world when he mentioned the awakening was caused by protecting Luffy.
You’re looking at conquerors haki as if it’s just the desire to conqueror when it’s clearly not.
Sanji has told plenty of times a desire for strength to protect as well as an acclimation towards leadership. I’m not saying he’ll get it I’m just saying discounting him for the reasons you’re mentioning doesn’t seem fair