They need high capacity magazines and rapid firing capabilities...for the exact same reasons that the police do.
I would argue that the definition of what is a ‘battle rifle’ is quite arbitrary to the times and the needs. The M-1 Garand was the best rifle of WW2 by many accounts. That standard is not what is considered the best today. A different set of ‘needs’ is desired, resulting in the M-4 or civilian AR-15, or AK.
It isn’t up to anyone but the individual what their ‘needs’ are. If I don’t harm anyone unjustly with what I consider my ‘needs’, then constitutionally nobody can define those needs.