The thing about research, especially interrogation, is that there are a LOT of regular getOneFree and protected topics. It makes sense to research all of those by interrogating the enemies where research is the cheapest, so that you don't waste the more valuable and more expensive enemies to these topics (and instead get more valuable information out of them). (You cannot rely on getting enough Secret Files, etc. to get these easily.) Compared to vanilla, how you progress in the research tree also depends a lot on RNG on which subsequent topics opens up.
For specific example, before going down the MIB path, you should clear all the protected and other available topics first (because MIBs are very expensive compared to the the others in the same timeframe). And before starting interrogating alien leaders, engineers and navigators, you've hopefully learned all the topics you can get from the hybrids, because you want every topic you get from leaders, engineers and navigators to progress the tech tree so that you can get access to better techs earlier. (Hybrids are also much cheaper than the MIBs.)
But it is certainly true are a huge number of research topics (non-interrogation) that don't progress the game, open further opportunities and are rather useless. You can and should definitely deprioritize these anyway (after playing once or twice, you learn them). But based on my experience, there is still a LOT that you must go through, and combined with all the enemy interrogation you need to do, I can't see how you could keep up even with, say, 100 scientists by the end of 1998. Or at the least you're handicapping yourself by not progressing as quickly as you could if you had made different choices on how much you put into research.
In contrast, in my current SH IM game, I had something like 250-300 in 1999 and over 400 scientists by the end of 1999. That was certainly a bit of overkill, because in the second half of the year, I only had a couple of topics left and I had already exhausted all the junk as well. But at that point I had nothing else to do with the money in any case, so why not. At least every new thing that pops up (in this case the topics opened up after advanced labs such as plasmas) were straightforward and did not need to compete with other dozens of more important research topics (for example, a space-capable transport).