One way to check is to navigate to the program change speed in the system edit menu: Select system edit (midi func menu is displayed) < memory protect < restore system defaults < program change speed (v or ^ toggles normal or fast).
@Harley, can you check this on your1.33 please and let us know if that version had the option.
What I do know, is my original unit was very slow and didn't have the option. Very soon after I bought it I was given a new EPROM which had the option (as I wasn't the only one complaining about it). And now I've read the EPROM update instructions (the other day) and they talk about v1.23 to 1.32, so I'm not sure if I went to 1.41 years later when I found the depot and MJMP had the 1.41 EPROMs and the option was available in previous updates. The default setting for program change speed is Normal so if you (or your brother) didn't change this setting, it would indicate the speed of Normal was improved with later versions (given your brother reports the improvement).
The other take away from reading the update instructions was to Reset System Defaults (to prevent garbage screens in real time midi edit). The instructions refer to Reset System Defaults, in 1.41 the option is Restore System Defaults not reset (and I don't recall ever doing this, but maybe I did, I would have followed the instructions).
It would be nice to know the EPROM version history and what changed with each release.
The 2 things I always check (and change if needed) when I've acquired additional MP-2s is the program change speed (to fast) and I activate the Stereo Volume Control (to use a MXC expression pedal).
@Harley, you said you didn't like the Stereo Vol Control, maybe it improved with 1.41? because it works really well for me. I didn't use it initially, I started using it much later.