I think you're misunderstanding the topic, the question isn't if RE are bad or why they are bad, but why they cost so much for being that bad.
RE were nerfed some time ago (april 2016) because one player used to spam them efficiently and win games in auto-match then balance team being what it is they applied the usual hammer nerf on them not trying at all to re-balance them.
Rear Echelons
We have scaled up Rear echelons up slightly to reduce spam.
Rear echelons cost up from 160 to 200
Rear echelon rifle damage up from 8 to 10
I like the slightly.
Then they received smoke as a nerf for USF since rifle lost it at the same time.
Then they've been nerfed again with the no dual M1919 for them and rifle (which was then true initial problem)
Then they lost 2 dps for a bit more accuracy. The true real reason was they were too good vs light vehicle with their 10 dps and no accuracy penalty. Kubel would melt and they could deal some damage to a 222 behind cover. another nerf in reality.
Then they received with the new doctrine the grenade launcher.
Somewhere in between they also received the flamer upgrade because removed from riflemen (another nerf), which has been a disaster for the commander relegating it into oblivion.
Really considering how much nerf the RE has received, the cost of 200 is really high. but on the issue of them losing to the pioneer rush in this above scenario that was counter, in fact, RE was misused. He shouldn't be alone there.