So... the setup was: Rear echelon and rifle squad behind green cover. Since those are tank traps, not the best kind of heavy cover but oh well. Beggars can't be choosers. So 280 + 200 = 480 manpower squads, against cheaper to reinforce and build, double Pioneers.
Now, I'm fully aware that the real scenario fight, in a real game I've had (2-3 games ago, something like that), was extreme RNG. In that fight, pioneers just refused to drop. First squad that retreated was 10% hp and 4 models, and the 2nd pio squd forced my retreat (I focused one squad at a time). So I've went on to test the double pio charging vs rifle and rear echelon holding ground.
Setup to mimic the fight that actually did occur in a game:
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Pioneers charged from behind the cover, while I was waiting with rear echelon and rifle, while the 2nd rifle squad was going around to flank the incoming MG42 which would, I presume focus down the echelon and rifle behind cover.
First test:
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With the pios, I focused down the rifle squad first. I'm guessing this was another example of RNG because pios should in no way-shape-or-form win with 5 models left alive. And due to the angle of approach, the cover was inconsequential. Also, what contributed to such overwhelming victory is the fact that for some reason, rifles got buggy. They were not firing as fast as they usually fire, I presume due to targeting issues. It seemed like they constantly were switching which model to target. So I'm guessing this is just one of those RNG moments.
Second test:
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This time less RNG, I actually did win, but at the expanse of losing a rifle squad. Now, how the fight would have gone in a ranked game... I don't know. I'd probably retreat rifles at 2 models, and he would retreat the pioneers at 1 model. Still would be somewhat of a win for him, because on my frontline it would be the useless rear echelon, and on his frontline, it would be an MG42 with the incoming gren. So this is a Pyrrhic victory.
Third test:
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Focused Rear Echelon first. Another Pyrrhic victory.
Fourth test:
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Focused rifles first. Also a Pyrrhic victory.
So this was done with the squads behind somewhat of a cover. I don't know how a cheap squad can gun down a semi-elite close range squad and another squad in their price range.
Pioneers should not really be combative enough to force such Pyrrhic victories.
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Now, I'm fully aware that their combat strenght falls down hard. But in teamgames, such fights dictate A LOT. The first few fights, where the RNG can swing in each direction, there should be some certainties. Like 480 MP with more reinforce beating 420 with less reinforce. Sure, pioneers can stay relevant up to minute 8 with the flamer, whereas echelon can stay relevant up to minute 15 with the zooks.... but still. Pioneers should get a buff somewhere else, and a nerf in their close range firepower.
EDIT/UPDATE: While I think that pio vision should be 40, not 42 (the only nerf they deserve)... after further testing, it's not that pios are strong, but that REs are dogs*it. I've placed REs behind green cover, on neutral terrain (sandbags on TestMap), and made PIOs charge them over said terrain... Pios won.
If you put Combat engineers behind green cover and let pios charge them, Pios lose hard.
So this is mainly that whatever squad you pair up with rear echelon, you can for all intents and purposes disregard the RE squad. It's like they are not even there.