Well the pure delta design has a High drag when compared to the conventional design with a tail plane. This is a known fact...here energy means 'speed'.
Due to the larger surface area of the delta wing the instantaneous turn rate is much higher comparatively but this creates a lot of drag.
The maneuver you are talking about is a barrel roll but the one I am talking about is the rolling scissors...where the lead aircraft has a tighter turn radius and the chase aircraft has a lesser one he climbs up and drops down on the lead aircraft giving him opportunity to lead the enemy with his fire and thus preserving energy(speed) in the dive.
What you talk about is the fight in the horizontal...but this is how they fight in the vertical. The Israelis have a similar maneuver called as the 'Let him pass' executed by the Mirage/Kfir against the MiG 21s in the Arab-Israeli war.