This would create other problems, it would make Creativity the main source of high tech. If you have 45 weeks to research a weapon the races with high creativity will get it sooner then the rest, indeed they may well get most of their longest techs this way. So you would need to either change or remove creativity.
Creativity is broken anyway - you can tech your way to a victory without having a single dime spent on it. At 'very slow', it used to take a hundred weeks for the 'tech victory' condition even with lots of research. Creativity TBH should still work as it does, but have a weight on each tech.
Secondly it would man if you spent a very long time going up lasers and one of the other races got full shields and whatever weapon system you would be extremely vunerable to that race for a very long time. Espacially if you did not have any defense to their weapon type. So for your plan to work you may have to condense to a single weapon and a single defense tech.
And what's he going to do? Throw shoes at you? Note that I said 'exponential' curve. That means that the first weapons techs aren't going to be much more expensive than they already are - and later in the game, as you get more research it should be easier to afford a change in weaponry.
I see what you mean, but I think you're wrong, because right now, you can just tech rush to Black Hole Eruptors and it serves the same purpose, only it's too easy. There's fundamentally no difference between rushing to BHEs and stopping at disruptors beacuse it's currently too tech-prohibitive.
I think you're reading too much into this, and I have to say that for expensive 'endgame' weapons, it would be absolutely no different from any other research. If I waste all my time grabbing advanced colonization techs, I'm going to get trashed by the fact that everyone else has better everything than me. Weapons should be the same way - you need foresight, planning, and intelligence (like, espionage) to be effective.