I agree with you totally - the other various games ramped up with you much more gracefully, so you'd have time and money to invest in the intermediate tech and use it in anger before progressing onto better tech.
At the moment, the steep ramping up of difficulty means the intermediate tech is pointless, and actually penalises you with the cost and time wasted - the corsair is an example of the geoscape combat, laser rifles for the ground combat.
I like the explanation of why you can use alien tech to speed up manufacturing. Once you have alien electronics and an andron autopsy, you could cobble your own production line together, and halve or quarter the time taken. The way I also see tech adoption, unless you really are improving the way the tech works from the ground up, there should be no reason to build anything from scratch - the most you'd do for an alien weapon is redo the stock, sight, trigger and grip. Your troops are being butchered with advanced weapons, why wait 2 months for research and engineering to make a human version?
If you think of the balance between research and engineering as it currently stands, I have 15 scientists that are mainly sitting idle since they finish research so quickly. On the other hand, 40 engineers still aren't enough to construct and keep pace with the alien ramping up.