In real life Pak guns are deployed well before the battle.
In RO the battle has allredy started and any Pak guns allredy in the map lose the element of suprise. Any Pak guns that are deployed in the battle need to be deployed behind the front line. This requires large maps with one team constantly retreating.
This means in each section of the map you will only get to deploy the Pak once before that area is the front line again.
Also, if the Pak is behind the front line, it will require at least one player to operate, wich means that he will be waiting for the front line to move back. This is a) defeatist b) a waste of a player who could be in the front line.
Then there are problems with deploying. RO only allows simple actions so the process of deploying would require a big change in the basic controls of RO.
Pak guns will not work in the RO enviroment.