Depends on the boss & the phase you're playing.
For example, Proxima Midnight has high Energy Defense that gets higher as your Phase increases. There's very little point in bringing strikers with Energy Damage if you have other options. Conversely, Cull Obsidian has high Physical Defense and is 100% immune to Physical Damage while his shield is up. Not much point in bringing strikers with Physical Attack.
Of course, this assumes you're actually relying on the strikers for damage. As your roster improves & the WBU phase increases, you tend to use strikers for their striker bonus & not for the additional DPS.