I'm a more-PVE-than-PVP boy in my WoW life (08/2005 to 08/2018, and back again in decembre 2020, doesn't liked BFA). My previous pvp (and pve) exp was at Legion S5 (2400+ in 3s as MW) / Tomb of Sargeras HC.
This year w/ the sanitary fail and a new house (youhouuuu) haven't the time to play raids 3-4 days per week, so i'm mostly pvping because it's easy to do somes arena every days. I'm currently 10/10 Heroic only, and have done most M+ keys in +11/+12, but 2100+ CR in 3s Bracket, have a mythic ilvl gear (225 avg ilvl) without killing a single mythic boss in CN, and without getting somes +15 keys. Haven't time for raiding (haven't guild LOL) so it's right good for me, I doesn't except more.
Actually the max avg ilvl in the game is around 228.5 and i'm 225. Ok, but everyone can't be at 2100+ in PvP, everyone can't even hit 1800 to get 220 ilvl.
There's no reason to scale ilvl from PVP to PVE or PVE to PVP. Both hightest rating got hightest item levels.
With mythic keys you have thousands items for the same slot, with different secondary stats. In PVP you have 2-3 items for the same slot, more for weapons if you swap your covenant (pvp vendor have differents weapons with differents secondary stats according to covenants). You can't really chose your gear, and even if you are Mistweaver like me, you need Crit/Versa, PvP offer a lot of Versa/Crit, but a lot more versa than crit, it's not optimized at all for PVE, it'll not replace a 225 gear with Crit>Versa optimization obtained from mythic raid or M+XX.