Human Ktulu, frankly I didn't really understand your post. I assume your question is: how much easier, statistically speaking, is it to get hand-held laser weapons than plasma weapons calibration?
Provided that your percentages are right, then (according to Dioxine's calculations) you have 18/1000 chance to get plasma weapons calibration in just 7 steps, as opposed to 160/1000 chance to get hand-held laser weapons. Therefore, you'll almost never get plasmas before lasers, and you'll probably have lasers much earlier than plasmas.
I'm still messing around with the tech tree though, so I'm not sure if Anti-Matter Containment should be necessary for hand-held lasers (and hand-held Gauss weapons). Perhaps UFO Power Source would be enough? Then you would get them some time in late March or April, I guess, which is definitely not as fast as in vanilla game, so you still have time to play with traditional firearms (first without, then with alloy ammo). On the other hand, that would mean we're losing the miniaturisation aspect: you have Laser Cannon, and then you can research Laser Rifle straight away, with no additional technology needed, which is a bit weird (hence Anti-Matter Containment was introduced). I would be happy to hear your opinion here.
A separate idea: now at the very beginning of the game, the only thing you can research before the first UFO appears is the Motion Scanner. I was wondering if perhaps you would have to research tanks as well, just to make things more complicated... But that would mean you'd have to produce them too. What do you think?