I highly doubt this, I'm pretty sure they design for mythic then start gutting it. I don't have any proof and it'd be interesting to read a blog about it but I highly doubt they're sitting around thinking about LFR. If anything they're brainstorming stuff like "What if the raid chased Sylvanas through chains surrounding Oribos?" and then going from there.
I think the second sentence is true but that's not how I define "hard". Running through the Yogg brain room without taking skull damage takes some practice and you can't sit in front of a target dummy and get that practice.Ulduar isn't hard. Nothing in Classic is hard. People will clear it in complete pug groups within the first reset