Right, but by my way of thinking at least you shouldn't be able to expend the Great Scientist on nothing just because you're a new player who hasn't figured out all the nuances to very nuance-heavy game. For example, imagine if you could click to expend a Great Engineer to "rush build" a spaceship part and then it would just use up the Engineer without actually doing anything. Instead, it properly just doesn't let the user do this in the first place.
I guess there's no real reason it would "have" to be this way, it's just odd to include so many combinations but not all of them. Like, 26 of 28 is weird. If there were 26 out of like 60 combinations I'd be just saying "ok they didn't want to put 60 civs in the game, I get that".
Some other useful stuff would be:
* The ability to look over the diplomatic or civics screen when you're challenged to make a change by some leader
* A little bit better unit queuing system that can slide stuff into the middle and not just either end
And I'll be fine if they never do any of this, which I bet they don't, but compared to other games around the same period that had more useful features like this at the time, or that have received updates since then, this one is a little lacking in some of those certain ways even though it remains a really good game (if it was a mediocre game I would just play something else rather than wanting a usability change).