That makes sense about the activation. Why bro-split though? It's been shown to be sub-optimal.I just jumped back to DBs over the past month. I went lightish but think I could've done the same volume. I think the idea of pre exhausting is to get a better mind muscle connection? Be able to focus on the chest activation more? I think it helped. Maybe building up the Work capacity now that I'm back to a Bro-ish split it'll get better.
Another exercise I just went back to is dips. That was my last chest exercise and surprisingly the volume was up to par with my old U/L split.
I love dips. But unfortunately, I had to stop them. A few months ago I increased my dips volume and then a few weeks later I got a flare-up in my shoulder that I could feel while doing flat bench and shoulder press, so I stopped the dips and did some rehab (dead hangs etc., and did supinated grip on the db bench for a while) to resolve it. I'm not saying it will happen to you, but it's something to be wary of. Google "dips shoulder impingement", you'll see what I mean.
My main for tris now is EZ-bar skull-crusher and I immediately super-set that into the same number of reps of close grip press, i.e. zero rest after getting to 1 or 0 RIR on the skulls.