I've flown out of Barton once or twice, along with some much busier AFIS airfields such as Popham rather more. I can't say I agree with SRG's conclusion. If a pilot was unable to make a timely finals call that was due to too much RT chatter and there may be a local RT discipline problem rather than not enough ATC.
I do agree totally with AAIB's conclusions about overtaking however, they are not supposed to criticise in their reports, but that comment is pretty close to it.
One point not made in the report, but I'd note reading the report and having flown a few hours in both types is that a PA28 has very poor visibility forward and down, and a Thruster has very poor visibility upwards and behind. I know it requires "thinking out of the box" a little, but it never harms to be aware of the characteristics of the aircraft around you in the visual circuit- something that looks also to have been lacking here.
G