On average, it takes an OEM around 12 to 18 months to bring a smartphone to market from scratch. You do the math.
Given those lead times, the folks in Redmond will not have had much (if any) say, at the time the most important decisions for these devices were being made. Once design objectives are set and work has commenced, you can't change things around without throwing the schedule overboard. If MS had, we'd now still be months away from a high end WM device.
My point: That idea that Redmond had little to no input on these hardware designs is not as ridiculous as you think it is. It's very likely 100% accurate.
On the other hand, calling these devices "leftovers" is probably a poor choice of words, as that implies they were unused designs that are only now being "served". That's not a good way of expressing that these products were just the latest additions to Nokia's development pipeline at the time MS took over.
Implying that the ex-Nokia team requires help from Redmond to develop good hardware also seems a bit galling to me. Hardware is the one area where almost everyone agrees (including WP critics) that WP devices were very good (read the Verge's original review of the L900). IMHO the Nokia hardware guys always made the most out of the software and ecosystem capabilities that were given to them... it's the OS and the ecosystem which has been tripping WP up. Not the hardware. If anybody needs help, it's the mobile OS group in Redmond.
Anyway, I agree. The 950/XL are underestimated. They are great successors to the 1520 and 930.