This is totally the type of climbing I steer clear of but I think I understand the "how hard is the scary bit" E-grade logic.
The bottom of WSS only feeds into the E grade in that it is harder to do the serious second half climbing after being powered out by having just bouldered 7B+.
So if someone climbs 7B+ fine but doesn't climb bold E4, they know to steer clear. If there was an amazing resting position such that the top only felt E2, they might give it a go.
What really didn't make sense was when bouldery bolted sport routes in the UK got E grades that bizarrely just followed a physical difficulty logic -simultaneously with us having unbolted routes that didn't. So you got an E6 tick for Entrée
-But no one gives sport routes E grades anymore.