Flexibility? You mean like hitting the field 5mins later so you can't even wire off key green cover or garrisons like pios or sturms can.
Maybe next time you make a post include actual stats and not out of date ones, your argument might be stronger lol
You seem to be misunderstanding the difference between flexibility and utility. Utility is being able to do things like wire and mine and scout, flexibility is being able to do that or other things. When pray tell is the last time you saw a pioneer squad scare off a tank? Or remember that time that pios got a mine sweeper and still had the same firepower they spawned with (4 smgs) but also 25% more health?
Flexibility is bigger than utility. Being able to adapt them to the role you need them is huge. They WILL be on or near the front because they are not a required unit that has a chunk of your pop cap sitting in base stacking stones so you can build a tank meaning sappers are there to offer a bit more pressure or jump on a crew weapon guaranteed because the only time you need to pull them back is to base is to keep them alive.