There is no issue with pioneers.
They are decent at the beginning, but fall flat on their face quickly. Spamming them is not viable, nor is even building a second one in the early game unless you're trying some odd double MG/double pio stall for PGrens.
In a normal build, you'll pay for it once LVs arrive until the mid game where you can finally use the increased repairs for your medium tank.
This overall sounds like a fair trade off to me, let them have their chance to shine.
I tested it out. It's basically that echelon are so criminally bad at combat, that you can basically ignore them as their DPS is laughable. Even at 10 range, Pios have 55% more DPS than echelon. Tested out Rifles + Combat engineers (soviet). Pios get wrecked. Tested out rifles + vehicle crew... pios lose hard. Basically, RE is completely useless in combat until you invest 100 munitions into them, at which point they can be used as a vehicle deterrent. Or you could use the volley fire and delay the weapon upgrades a bit. And I wouldn't call them useless later on. Not only can they repair tanks quite fast, they do get the flamers and they can plant mines. Double Pio with MG42s can easily stand up to anything in 3v3s. Mostly due to map designs. Tightrope even showed the power of double pio into PGrens power.
So all in all. The fight should say "Rifles" vs double Pios. Rifles + Rear Echelon = Rifles -> Rear Echelon = 0 iff Rifles =/= 0