Lol, I'm sure that you've mastered whatever elo you play at with Udyr jungle, but I promise you that what I'm telling you is how it is against opponents who know what they are doing. If you don't build damage on Udyr, you're irrelevant in team fights. If you rush damage, you're going to get kited and die. I said it's not debatable because it isn't. Udyr is a horrible team fighter. No one argues that fact except people who have never played against competition good enough to make Udyr's flaws frustratingly obvious. I could play Diana jungle in Bronze 5, faceroll the enemy team and talk about how great Diana is, it wouldn't make Diana a great jungler lol.
Udyr can't initiate anything unless you catch someone way out of position because he doesn't have hard engage. If you do, it isn't because Udyr is a great initiator, it's because they were bad. The best Udyr can hope for as an initiation is a flash stun, but that leaves him without flash for the next 5 minutes. If you take Ghost, you have no initiation.
If you try to get to the carries you should be CC'd and killed.
If all you do is try to get stuns off and eat skillshots you'll do no damage.
If you try to get through the front lines first, you'll do no damage to them and since they probably have tenacity your stuns won't be worth mentioning.
Against bad players all of this means nothing, but if you expect your opponents to have any kind of in game sense, especially in a pre-made 5, you should expect to be useless in team fights as Udyr. If every jungler I listed + 3-5 more was out of the game for some reason, Udyr would be a top tier jungler. As of now he's tier 2 at best. He wasn't even top tier before the nerfs to feral flare. Now he's nothing more than a gimmick champion.