Is it better to level from uncommon up to the highest or does it work out the same as finding loot?
ie I leveled up to rare on pants and they’re 415 armor
found some Epic and they’re only 71.
If I level the Epic will it end up the same if I keep leveling the rare?
Levelled gear and found gear follow the same base stat rules so it doesnt matter.
The difference will be chance: which attributes and mastery does one piece of gear have than another. Whether you found it at Epic, or levelled it to Epic does not influence those results.
EDIT: one small caveat - a level 1 uncommon gear will have lower base stat than a level 1 Epic gear, but the same two gear pieces will have the same base stat once they are both equivalent level and rarity.
So Royal leggings found at
LVL 1 and level 30 will both end up at say 1000 armor despite the 30 being at 71
exactly, yeah I added that to my post to clear up that example 
I saw your post after I posted. Thank you for your reply!
Sort of. Rarity is what makes the difference, not found or leveled up. Mythic > legendary > epic > rare > uncommon > common.
To clarify, rare items at level 5 will always be better than the same item at level 5 if it’s common or uncommon. Once they’re all rare or whatever, they’ll all be the same.