I believe the vehicle parameters and performance should be exactly the same in both modes.
Strictly speaking, Realistic Battles are not a more advanced or superior mode compared to Arcade Battles. RB simply better fits the fantasy of a military simulation, while AB better fits the experience of armored combat and direct tank engagements.
War Thunder is unique because it can satisfy both types of players at the same time. The only real difference between the two modes should be the information system — mainly the presence or absence of enemy position markers caused by different levels of battlefield information sharing.