No. Pioneers with flamethrower don't perform well enough because this squard has poor durability,you simply lose 2-3 models fast and have to retreat.The flamethrower poineers/combat engineers/rear echlon never become problems. Because they are the weakest infantry of the whole game.
At least royal engineers have much more firepower due to their sten smg,they can even force back a grens squard 1 on 1 in close combat.
The thing is relic just don't know what they are doing at all.Leave the weakest infantry(poineers/combat engineers/rear echlon) alone at low pop cost because there's not a single reason to spam them.Increasing the pop to 6 makes no sense because the mainline infantry has 6/7 pop cost.
The flamethrower provides anti-garrison damage and anti-cover and one it isnt about what they can fight in 1v1 Company of Heroes is a game of combined arms and using a mixture of units so its what they provide to the army and the pioneer fills in many roles in the Wehrmacht army not filled by other units (That is part of the Wehrmacht army) with only a few others that can fulfill it such as the Flame Halftrack which is really expensive and more dangerous to use
The flamethrower is available from the start of the game and is useful thoughout the entire game on maps with buildings
The Royal Engineers just provide a cheaper alternative to the infantry section they dont add anything else to the army they are just a cheaper alternative like Ostruppen
To make it clear Pioneers can fill in more roles than Royal Engineers while Royal Engineers may be good combat units for an Engineer unit they dont fill as much roles