The pros have very diverse picks in every worlds with a changing meta. Seems like pro junglers get locked into a very small pool of champions however.
Sej (although not much this worlds Olaf Rek said Gragas Lee sin J4
And maybe a couple I am forgetting.
Every once in awhile another pick becomes meta till they nerf it out of the jungle (ezreal ivern, or camille) or they buff Lee sin again till he is back in the meta
I wish we saw some different champs this worlds
there was skarner a while back, until riot decided to buff leesin again because whynot
One more champ you forgot is Elise. She usually is good enough with CC and burst to be in the meta fairly regularly. Every now and then a pick like Nidalee, Nocturne, or even Graves gets a little use, but yeah, is seems most seasons there is a pretty locked in pool for jungle. I'm hoping the Volibear and Fidd reworks put them into pro play. They may end up like WW though, good for solo Q, but not desired for 5 man teams.
The pros have very diverse picks in every worlds with a changing meta. Seems like pro junglers get locked into a very small pool of champions however.
Sej (although not much this worlds Olaf Rek said Gragas Lee sin J4
And maybe a couple I am forgetting.
Every once in awhile another pick becomes meta till they nerf it out of the jungle (ezreal ivern, or camille) or they buff Lee sin again till he is back in the meta
I wish we saw some different champs this worlds
Oppressive, high burst, early game pick junglers dominate worlds because the fact is junglers as they are designed fall off HARD. They are always underleveled compared to laners and their smite item will always make them statistically inferior to champions who can simply sell their doran's and get 6 full item slots.
So as a jg you play champions that can give priority and have impact on the map early.
Farming junglers will never be a thing. Games are decided early and objective/lane priority makes them irrelevant.
Assassin junglers won't either because why be an assassin when a Lee Sin/Gragas/RekSai/J4 does as much if not better damage early on than them while being more mobile, survivable, and has CC on top. There is literally no point to Rengar/Kha'Zix when Rek'sai/J4/Lee Sin do as high burst if not better than he does with far better perks.
The jungle meta will always be centered towards early game CC burst junglers because the jungler's role is to be a secondary support to laners instead of being a full fledged champion.
is always meta since he get buffed before every World. Wouldn't want Mr. FlashyhopwardskickLC$ to not get picked.
As for 
, he crowd most of the jungle picks and almost become 100% pick as soon as he is viable.
Jungle is probably the hardest position to have high diversity.
I don't even think jungler diversity in proplay is that big of a probleme. Aside from the jungler you've mentioned, there is also elise, taliyah, and qiana, who are often picked as junglers in this worlds alone.
I know that is not that much diversity, but other roles are exactly the same. In current worlds adc is xayah vs kaisa every game and it's awful. And I don't even want to know how many patches made midlane into Ryze-Azir-Corki-Meta for proplayers
Gragas this year has been a full AP gragas every time. I don't think it's the same as the tank gragas we had in earlier seasons.
Thats just the state of the JG right now, especially at the highest level of play. Because you don't really have the resources to actually scale this season you basically have 2 choices, pick an earlygame power jungler (Olaf, rek-sai, and to some extent Lee fall into this category), or you pick a champ that can still be impactful on lower jg income b/c of the engage in their kit: Gragas, J4, sej (also to some extent Lee b/c of insec).
One champ I would like to see in pro play is, Kayn. Not because I main him, but because his Q recently got buffed. Kayn also counters a couple of champs in the pro play meta as well.
The champs you listed work well with a lot comps and are very useful in coordinated competitive teamplay. A power farming yi or udyr cheese gank will not work well in a competitive environment.
