I think it's more realistic the way I suggested, because Paks didn't change positions that much in the very heat of a battle as RO is modelling it. And usually, after one tank is hit the others knew the position of the Pak, it's ok if they come to take it out the next spawn
Talking about mobile, if it will have to be mobile; then it have to be modelled the realistic way. How it will be mobile? If the pushing it will be modelled, it will be damn slow. Also, pushing it against an elevation should be impossible.
If the towing by the vehicles will be modelled, then a realistic time to pack, unpack should be there. Taking into account the fact that even some players are against realistic supply time, I think making them mobile will be worthless in the eyes of the players. So, you will have to choices.
1.Make them immobile and placed before the rounds(Realistic way)
2.Make them mobile, but somehow "more mobile"(arcady) from their RL counterparts.
Also, if Pak's are going to be added, then vegetation should be modelled more intensely in maps. It's a must. Put a Pak anywhere in Orel, and you can spot and kill it accurately from 2km
Same goes to MG's, but it's not very noticable and they don't need it as they are mobile very much.
I also want to add that Paks should function with two players. One for aiming and other for loading. The loading should be made more attractive, something like skill based loading system should be introduced. Think it like how you make foul shots in NBA series
It may even be the base of adding tank loader class.