USF isn't supposed to rely on RE.they are not meant to be an alternative to rifles. They are not supposed to be able to fight anything unsupported. Their job, as the name may hint towards, is to be in the rear. They are basically ostroppen teir that trade squad size (and thus combat power) with utility. They can do a lot of they have to, but none of it well. They are stop gap, reserve infantry not combat infantry.
That would be true if pios were the same or CEs for that matter.
Rear echelons have one early game utility... lay tank traps.
Tank traps are useless vs MG42s because they are so weirdly modeled that the MG42 will always suppress in a burst or two any squad behind the line of tank traps (2+).
They are decently useful to hold against pushes, as they are green cover, but besides that, useless (ok, harder to destroy than sandbags).
They lay useless mines.
Their only real useful utility are the caches (later on) and carrying zooks to deter P4 dives (even later, after BARs).
Now I've done the tests and I found the following:
Rear echelon behind green cover, solo pio charging over neutral cover: Pio wins with 2 models remaining, echelon retreats with 1 model. Only way to stop is to use muni for the volley.
The test where Rifles charge pioneers behind green cover, over neutral terrain: Rifles win with 2 models remaining on average, pios retreat with 1 model.
So on one hand, an engineer unit can charge another engineer unit and win easily, but a mainline unit doing the same thing to the engineer unit (pioneer) will win a Pyrrhic victory. You will bleed more than pios, and let the incoming grens/MG42 do the job easily. God forbid you play on a lane-y map where you can't flank and the MG42's wide arc can easily cover 2+ points.
The first skirmish is echelon vs pio, pio wins. By the time your rifles come to the frontline, so does the MG42.... good luck. If you decide to wait for the rifles to join the echelons to have a 2v2, then you're in for a treat because on most 3v3+ maps you really need to take the long way around (grens come) to flank. Not to mention that you need to chase down an MG42 while pios are closing in and putting a hurt on you.
Also did the following test. Pios vs rifles, pios come around the sight blocker (test done on beach Across the rheine, bushes around the neutral point below the hill).
Rifles standing still in neutral cover, pios come from neutral cover and the whole skirmish is with both units in neutral cover... just to show the close range power of pios... pios retreated with 1 model, rifles with 2 models. 4 times in a row... 4 model pio put a hurt on 5 model 280 MP rifles close range, neutral cover.
One thing I've learned from experience is: If you are fighting rifle + echelon vs pio + gren... And the pio is charging... Even if the grens are in red cover, focus the pios first. If they get close enough, both echelons and rifles will go down quickly. I know because it happened to me last game. Didn't even notice a pio charging, both rifles and echelon were behind yellow cover ( I was fighting on a different part of the map and I can easily press "1" and "T" in case of a rifle nade). Rifles and echelon were firing at the neutral cover gren, while pios literally mowed down both echelon and rifles to 1-2 models each, as they closed in point blank. Close in point blank with echelons and you'll have enough time to boil some tea before echelons kill anything
Of course, as time goes by, you get the flamer to scale, at which point rifles lose until double BARs come (or win a Pyrrhic victory). Later on, there is no way for the pios to win in any way-shape or form against rifles, as expected. But the opening skirmishes in teamgames, OST is vastly superior to USF in 90% of scenarios. Heck, if I see that I have a spawn against OST on a lane-y map in my VP lane, I just ignore it and help my teammate 2v1 on the next closest lane.
Not only are most green cover positions designed for 4 model squads, but the idea of rifles being short range specialists makes them useless in long range cover to cover skirmishes against grens and MG42. Only those long tanks/pick-up truck/sandbags green covers can actually fit a whole squad of 5 models (hence why volks have sandbags).
Most green cover objects will deceive you and you'll get insta suppressed, or you'll lose that one model very quickly. That + the fact that tank traps are completely unreliable really shows why USF is seldom played in higher ranks and why you really need to put a lot more micro into your gameplay to win teamgames. Retarded map design coupled with rifles being only good on close range (exceptionally good, but so are pios/spios)
So in the end, REs don't really have early game utility. They don't have late game utility in the form of mine planting. Their only real utility is the fact that they can carry double zooks, which can be used defensively against tank dives. And it's not like those zooks are free on them. It still costs 100 Muni and can often mean that you won't be able to plant doctrinal mines or use other abilities as much as you would want. If they had a 10 muni smoke that doesn't require teching, then all would be well, but they don't. They are not only useless early game, they are not very useful later on as well (let's be honest, how many times zooks penetrate on anything tougher than a flakpanzer, if they even hit).
I know a lot about RE zooks as in 90% of games I play the heavy cavalry and I do have double Rear echelon in late game with 4 zooks (repair and anti dive). Trust me, if you plant mines with rifles, you won't have for the zooks, nor will you have if you decide to use WP from howitzers or nades/snares. Average muni income is 35/min in 3v3s on a good day... Good luck.