The Red Sox farm right now is juiced with prospects who project in the 3-5 starter/very good reliever range but lacks any true top of the rotation starter prospect. Lets be honest here, Barnes, De La Rosa, etc. are not Jon Lester or Clay Buchholz level prospects. Barnes for example is behind pre-cancer Jon Lester's career track record, who at Barnes' age was posting mid-2's ERA stints in AA and AAA with 15 MLB starts to cap it off. Buchholz was even fruther ahead at 22 as he was pitching at similar tiers but with far better success, including ungodly sick peripherals. Of course these guys have mitigating circumstances (Barnes played three years of college ball, De La Rosa had his tommy john issue), but the fact remains we aren't looking at the same tier of top pitching prospect here as there's still a lot of unknowns surrounding even our best pitching prospects.
The second bolded quote is more than a "mitigating factor"; it makes comparisons to Lester, at this stage of Barnes' career, 100% useless on apples-and-oranges grounds. It would be exactly as meaningful to turn it around and compare how they did in A+. Lester, at A+ Sarasota in 2004, had a 4.28 ERA in 20 starts, with a 2.62 K/BB ratio. Barnes, at A+ Salem in 2012, had a 3.58 ERA with a 3.64 K/BB. Therefore, Barnes is going to be a better pitcher. "But," you'll say, "Barnes was two years older!" And I'll call that a "mitigating factor."
It may very well be true that Barnes doesn't have the potential to produce on the level that Lester has, but their career arcs so far have been so entirely different that I don't think you can use age-by-age comparisons to support that point.
As for RDLR, there we do have the materials for a bit more of an apples-to-apples comp.
At 18, both guys pitched a handful of rookie-league innings, posting identical 13.50 ERAs.
At 19, Lester was in A ball, pitched 106 innings, with a 3.65 ERA and 1.61 K/BB. RDLR: FRk, 47, 1.71, 2.43.
20: Lester A+, 90, 4.28, 2.62. RDLR: Rk, 16, 6.06, 2.00.
So far Lester's well ahead; he's struggling a bit, but at A+, where RDLR is still in rookie ball and not pitching much (injury?). But now things get interesting:
21: Lester AA, 148, 2.61, 2.86. RDLR: A/AA (even IP split), 110, 2.37, 2.47.
22: Lester AAA, 46, 2.70, 1.72. RDLR: AA, 40, 2.92, 2.74.
Both pitchers were called up to the big club in the middle of these successful age-22 seasons. Here's how they did:
Lester 81 IP, 4.76 ERA, 1.40 K/BB
RDLR 60 IP, 3.71 ERA, 1.94 K/BB
Both pitchers, of course, then got whacked with serious health/injury issues that kept them off the mound for most of the following year. But at that point, they were pretty evenly matched. Lester had gotten a better head start, but Rubby caught up quickly and in his age-22 season appeared to be pretty much Lester's equal if not a bit ahead.