Yep, you know it all.... So you know that what makes a good engine is more than only a displacement.
As with 4 stroke engines you can modify the cam shafts for more performance you can do the same with 2 strokes with the port timings and with the crank shaft timing. The HPI engine is a cheap Chinese produced egine so by default the engien is lower timed so the engine will stay alive. Of course you can open up the crankshaft, raise the ports and drill up the carburator but with the 1st run the engine will shatter in pieces due the chosen weak materials.
As you are probably known with tuning parts like 7068 aluminum rods to even titanium and special light weight pistons (wich with 2 stroke are almost impossible) we do not have such option parts for a cheap build HPI engine.
Competition engines are first of all much higher timed, many of todays onroad competition engines can hit almost 50.000rpm while the HPI will not even reach the 40.000 rpm but maybe 35.000rpm. But second of all, the used materials are well chosen to withstand all the high G-forces at such a RPM range and there is even room to do more with open up the timings.

On youtube amoung bashers there is a buggy .28 challenge going on, who can reach the highest speeds. For one of those guys I have done an old Novarossi based .21 (!!) offroad engine. I did gave it an onroad competition spec timing with a tiny bit more degrees timing an managed to gave it 2 extra small exhaust ports. He did reach the 100km/h goal he wanted and that with still the stock 9mm carburator and pretty normal 25% nitro. That is more than all .28 setups up on today in that challenge have done.

So yes, I know a bit about engines too but maybe that is because for about 10 years I was involved with the devellopment of such RC engine. Not only as testdriver played with timings but also with a clear insight of material choices and designs of shapes and other stuff..