I have absolutely no idea how Tidus can be called whiny. As a child, his father was very abusive, being neglectful and not offering anything remotely approaching positive regard, nevermind unconditionally so. And yet as a teenager he is an optimistic, upbeat, hugely successful superstar. The most famous living person in his world, probably.

Then, when he is torn from all that, does he collapse into a blubbering mess? No - he makes his way around a dangerous, ancient ruin, fights some monsters and successfully evades something that could swallow him whole, gets a fire going, and is trying to figure out how to get some food. Then he is kept on a cold, wet metal deck by people who don't even speak the same language as him (and the one who does seems to have marginal influence), which is attacked AGAIN by the massive world-ending thing.

Thoughout the whole game, with what, one or two exceptions, Tidus is relentlessly upbeat, optimistic, and a hell of a lot closer to Sephex's macro than whiny. Most of the time the very worst of his "whining" is "this sucks but Hey guys we can do it! Let's GO!" The height of his 'selfishness' is wanting to go home and he pretty easily accepts that if it's going to happen, it's a long way in the future. The only time he actually cries is when he's confronting his dad, a man who raised him with neglect and abuse and then disappeared, leaving his mom to raise him alone until she died of despair after which point he was an orphan at what, age 8?

Obv. it's a matter of taste and feeling but one criticism which does not stand up to scrutiny is that he's whiny.