There’s a lot of threads on this
Just search the forums for ‘Heirlooms Azerite’ if you care to see the discussion about it but long story short: Azerite gear has more stam + survival traits on it so you are more durable if you aren’t wearing heirlooms. The suggestion people usually give is “wear azerite to quest and swap to heirlooms to turn quests in”.
Besides that my other suggestion if you aren’t a story person or looking for rep is to make a starter account (it’s free) and invite yourself to a group with a level 1 on that account and then enable party sync and you can quest anywhere in Azeroth and everything scales to your level but you play as if you were 60 so no 75+ talents or any abilities after 60. You will also occasionally get party sync caches that have level appropriate gear in them.