All I really have to say is that after a certain point kraken becomes a battle of attrition and doing that repeatedly will begin to affect the health and wellbeing of the players. We're all mmo players here and know how long content can end up lasting, I used to play FFXI and there was content that sent people to hospitals because of how long it took and it led to the games developers stepping in and changing or nerfing things.
I've had my fair share of excruciatingly long krakens, theres a lot of great pvp but it turns into people using rat tactics until the other sides are tired enough for them to kill it. Somewhere between 4-6 hours would be an ideal despawn timer. With a more strict despawn timer people can still get great pvp, but they'll also be forced to try harder to take kraken in a reasonable period of time or develop new tactics for them to take it.
Kraken doesn't need to be nerfed, if uncontested it can literally take less than 10 minutes, but the despawn timer definitely needs to be adjusted. Just my two cents.