You keep saying this, and it just sounds more ridiculous each time IMO. So I'll break it down for you:
1) Shoemaker regressing to a 3.7-4.2 ERA range is a possibility. He came out of nowhere last year and it's a small sample size we're operating off of. Personally I think he'll be in the 3.5-3.8 range. A solid #3 starter
2) If anyone says Richards will regress to the ERA range you mentioned they are batshit crazy. BUt I don't believe anyone ever said that. 2.8-3.4 for him IMO
3)Weaver's trend since his dominant 2011 season:
2011:235 innings pitched, 2.41 ERA, 1.010 WHIP, 7.6 K/9 (one of the best pitchers in baseball)
2012: 2.81 ERA, 188.2 innings pitched, 1.018 WHIP, 6.8 K/9 (Still one of the better pitchers in the league but dealt with injuries and struck out less batters)
2013: 3.27 ERA, 154.1 innings pitched, 1.140 WHIP, 6.8 K/9 (More injuries and worse numbers across the board - still put up solid #2 numbers)
2014: 3.59 ERA, 213.1 innings pitched, 1.209 WHIP, 7.1 K/9 (It was great to see him pitch every game, but again his numbers declined. Solid # 3 last year)
Do you see the trend there with Weaver? I like the guy but he's in decline. I'm expecting a 3.6-3.9 ERA from him next year which would be fine
So no, not "just because". People aren't expecting him to be a #2 because he wasn't last year and he's got mileage on his arm and is aging. CJ being a solid #4-5 we'll just agree to disagree on.
Shoemaker is the only debate that's interesting. I could see him getting figured out next year or he could continue to be great. We'll see