How do stats work in new World of warcraft expansions?

i have played on retail for a short stint but not cross expansion. ive been wondering, how does expansion works?

i heard that at the new expansion shadowlands, the max level has been reset to 60 and stats reset to vanilla like, does that mean that if am a lvl 80 player still in wotlk, still grinding lore and quest to kill lich king if i run into a lvl 60 I get to kill shadowlands expansion player easily ? since my stats is lvl 80 versus lvl 60 stats.

can anyone explain to me how does expansion work in general ? I am a bit lost.

From Vanilla up to WOTLK stats was increased rather slowly and nicely but then "Cataclysm" came and all stats went overboard, and the expansions after that followed the same pattern, eventually it got so ridiculuos they probably went "**** it, lets go back" and scaled everything pre existent loot down to super low stats so they wouldent impact the newer expansion.
WoW have allways expermiented with stats, in Vanilla you can se some items with really wierd stats, in TBC they had Bonus healing and Bonus damage on items.
WOTLK went overboard a little bit with the Armor Penetration at the end.

I have a friend who plays retail and his Protection Paladin crits 30-40k on different abilities, so if you put a wotlk lvl 80 vs a retail lvl 60 I have no idea. I stopped following retail info some time ago, Dont even know he name of the newest expansion..

You should ask your question on retail forums, or reddit, since it has nothing to do with Warmane. But, short answer : No, you can't, everything will be scaled down.