There's team roles that are mandatory on every bulky offense/balance style team.
Namely a rock setter, hazard remover, speed control, and physdef/spdef pivots that usually overlap with the other roles. Every team also needs good ground/electric/and water immunities/resists. Once you've got these things covered the rest of the team slots go to offensive wallbreakers.
If you look at gen 8 that sort of "team backbone" ends up looking like a four mon squad of Dragapult/Corviknight/Clefable/Seismitoad with the remaining two slots being delegated to strong breakers for breaking through opposing defensive cores.
In gen 7, scarf landorus can combine both the speed control and hazard removal roles while also covering the necessary electric and ground immunity and acting as a physdef pivot. Combine him with a SpDef water resist and you've got every role covered except a stealthrock setter.