All true and valid points, but essentially beside the point. When people point out that Reagan would be considered a moderate today they are generally making the same point you just made: the right has shifted dramatically to the right since Reagan's day. In Reagan's time, the today's right wing politician would have been considered an extreme, fringe candidate. Not much different from a John Bircher.
Except that's not the point I'm making at all. Its not that the right has "shifted dramatically", its that the world as a whole has shifted and changed. I don't think the ideology of "the right" has shifted all that much since the days of Reagan. I think the desire or feeling of necessity to compromise has shifted, absolutely! I think the willingness to veer from ideology in hopes of getting some of it implimented has shifted. Completely! The realities of the past 20 years has caused that shift, not some heightening extremism within the Republican party. Take the Republicans of the 1970's and 1980's and place them in today's world, with the full context of what has happened over the past 20 years, and I don't think they'd be any different than many of the Republicans now. The ideology hasn't significantly shifted, its largely been the political PROCESSES viewed as acceptable or necessary that have shifted...and for good reason!
Take Deacon Jones from the 1960's and drop him down onto the St. Louis Ram's of today and he'd be an average lineman most likely. He'd be no match for the speed, quickness, strength, and all around athleticism the majority of left tackles in the game have today. If you want an 80's analogy, you could take Lawerence Taylor as well in a league that has learned more how to deal with extremely athletic and powerful line backers, he'd probably be a good but not a top 10 player of all time. Put them both in the new NFL with rules against hitting the head of the quarterback (This was a STAPLE of Jones game) or the mass amounts of rules for protecting QB's and WR's from head hits and unnecessary roughness. Part of what made Taylor great was the intimidation factor, yet that'd be reduced a fair bit by modern rules as he would be thrown out of games for spearing heads.
However...take those two guys, give them modern training throughout their life, give them experience playing under the rules of the NFL today not of the 60's and 80's, have them understand the game as its played today...and you're likely to see them become Hall of Fame level players in the modern NFL.
This attempt to take Ronald Reagan in the '80s and place him into the 2010's and expect that to be some direct correlation is like trying to place Deacon Jones opposite Chris Long on the Rams and proclaiming that he'd be considered an average to good player now.
Yes, I get the point that people, typically the most hyper partisan of liberals, are trying to make by pointing out that they think Reagan would be considered a moderate today (pointing that OPINION out as if its fact). I also get that their point is full of holes, flimsy, ridiculous, and stupid.