I think bruisers are about sticking to enemies and dealing damage rather than taking damage or denying enemies from dealing damage. For example Stiches damage is much lower than Imperius but he is generally tougher and has access to abilities that can zone or displace enemies to help the flow of battle in his teams favour. Imperius has more damage and can stick to enemies reasonably well, but will struggle to prevent enemies getting to his team’s back line and also cannot as effectively displace enemies that do.
Stiches is about enabling allies to deal more damage while taking less. Imperius is about duelling enemies and dealing and enabling damage in general.