well im very aware not every player 
but i can tell you from the other end as someone who does progress M+ and has Raided (not this expansion as much tho) I dont want to do as ltitle open world content as possible XD.
tbh its been a long time since iāve levelled a char without the boost serviceā¦ whgich starts you at 390. so my estimations maybe alittle off.
I was just looking at
- beginning Naz quests give you 25 pearls freeā¦ spend this on 5 Pieces (that u didnt pick as a Reward) it also gives a 370 weapon.
- Legendary cloak gives u a 480 Back piece.
- Azerite level is Super easy to raise getting ur neck to match your cloaks ilevel wouldnt be too hard.
- Any additional Pieces u can buy pretty cheaply at 400 ilevel from the AH.
- World boss gives u a 455 Piece, use your Bonus loot here
- Naz World boss gives u a 415 Piece use ur second here (one of the bosses drops a 415 weapon)
Discluding Chances at corruptions Which can vastly increase ur character power.
Iāve always found the base of BFAs open world (zandalari / Kul tiras) to become exceptionally easy upon 390ish.
normally in the first day of boosting at 390 ilevel, im normally roughly 440-450 by the end of Day 1 realistically.
For example. this char im on now I boosted Last saturday, i Pushed to a +13 Mythic before Reset in my first reset, and Now cleared a +12 in line for the next reset. and now im 460. all off the back of 0 Premades, 0 Use of boosts and Purely off grinding my face against M+ Pugs.
Lost alot of keys but i got through itā¦ but i was the lowest DPS XD i was doing about 35k while others did 60-70kā¦ to my suprise Not many really cared tho.