"It is obvious that pike due to being held in both arms will deal more damage than spear held underarm in one hand,"

A) Sounds more like Pike vs Lance

B) Does no one ever think about application vs situation in all these discussions? There are different pikes, and different spears, and they don't necessarily serve the same function or purpose. That's just my two cents.

For another source, Plutarch wrote that sarissas at Pyda pierced through all opposing shields and armor.

yes, i read that, thing is, at Pydna Roman losses were reported quite low.. just about 200 dead and wounded. and even if the actual number was 10x higher, it is still relatively low number if we assume pikes had no issues to penetrate shields and armor..

My thesis is that Pike was only able to penetrate shield and armor if it used the mass of men holding it and moving forward. This way, body mass and speed would increase the damage potential high enough for pike to pierce shields and armor, but once Phalanx stopped, and pikemen relied on their thrusts, they were no longer able to pierce shields. therefore they adopted tactics of pressing pikes against Roman shields so Roman legionaries couldn't get closer through.. with several pikes pressed against single shield, Legionary would be completely blocked, and even if he tried to cut of pike heads, it would not help him that much as pike without head can still be fixed against the shield to prevent him getting close... this is also something Polybius mentioned in his description of Pydna, and would explain also relatively low casualties on Roman side.. Phalanx once stopped, was good for fixing the enemy in place, but couldn't defeat more mobile Roman Maniples. Their only hope was to flank Romans and attack them from rear with cavalry, but Macedonian Cavalry at Pydna just routed and ran away...

One of the issues about pike fighting for me was how to create the impenetrable hedge.
It is an option to have each rank armed with a pike hold the pike in a different grip on its length in order to align as many points of different ranks as possible at one focal distance. Taking such an approach some pike points will be powerful pushers from the rearmost ranks that hold the butt end at the hip, while others in the front rank hold the pike at balance point and are better at fencing for the gaps.
Discussing pike performance needs to take into account the grip due to the tactical use.