Currently, there's little need for squad leaders to change squad types.

An assault squad leader can drive an APC, pilot a helicopter, be a sniper, and so on.

I think this is a very common occurrence. It seriously disrupts the mechanics of squads designed for specific missions.

Players join a squad and want to perform the tasks the squad is designed for.

Even in real life, tankers are unlikely to pilot a helicopter, and Arma strives very much to simulate real life.

Perhaps it would be worthwhile to add restrictions on the vehicles they can occupy and the tasks they can perform, perhaps as an experiment for certain servers.

I'll list the restrictions below:

1. Infantry squad commanders and subordinates cannot occupy the driver/pilot seats, only passenger seats.

2. Pilots/drivers of BTR and BRDM cannot drive other vehicles. This will help with the creation of missions to rescue the crew of damaged vehicles.

3. Any soldier can take the place of a killed crew member if there is no living crew member in the vehicle. Don't forget that this is still a game ;)