If I was the highest performing member of my team and I was thinking of leaving they absolutely would.
But you're using the 'any player' trick again when at no point have I said we should be giving every player everything they want, so please stop putting words in my mouth.
We should be valuing him as one of the most important members of our squad, because he is. It's why he's now vice captain, because of his standing in the squad. So why shouldn't his compensation reflect that? To use your example, if I became the second in charge at my company, but I was only 22, I'm pretty sure I wouldn't be told "Well we think you're very important to this company but because you're only 22 we'll pay you as a 22 year old would be paid".
He's probably been offered more than Coyle. It's not quite as simple as being 'second in charge' or 'second most senior'. He isn't, he's vice captain - same as Coyle being captain doesn't mean he's worth 30k a week like Seri and Tufan.