Oh they're great to get into the heads of the designers. You just have to read between the lines, ignore the pages of fluff, and keep a bit of rawhide nearby so that when the red mist starts to descend you have something to bite down on.
There are gems in there like how they decided there were too many elves and no one needed more than like 3. So they chopped them down to Eldarin, High Elves, and Drow. Because as they put it, all the other types of elves were just "variations on high elves". And reading that was when my brain just kinda shut off for a minute and I came to with the taste of tin in my mouth.
There's other stuff like their excuse for not including gnomes as a PC race option was because they didn't see the point in them. But they explain how tried so hard to come up with a reason to but couldn't think up one.
And I'm trying really really hard not to be a sarcastic ass while writing this. That's how bad some of these excuses are.
OH I almost forgot. Perkins wrote the section on "why teiflings got added" where he was supposed to explain why they added tieflings as a core race in 4e. Basically they were explicitly intended to be the default race pairing for warlocks, and that they were supposed to be the edgy chaotic troublemaker race for people who wanted to play crazy, edgy characters. Also it reads like they were getting sick of Drizzt clones and tieflings are meant to be a way to distract those people into running something else. At least that's how I read these bits: