Do you really think the ilvl DR system is why Rated PvP is unpopular?
One among a few reasons, absolutly.
Other games (like Overwatch, a real PvP game) don't have any element of grinding combat advantages, why would arena need grinding combat advantages to draw players?
You're projecting your expectations of "what players want" across different genres.
The players that PvP in WoW aren't the e-sport player MOBA player or elite FPS player.
It's the MMORPG player that enjoys PvP.
Comparing WoW to Overwatch is the problem in itself.
In this failed atempt of pleasing a crowd that is not the one that plays WoW, Blizzard alienated the WoW playerbase that could be PvPing.