Recorders are bit boxes, storing 1s and 0s. That is all they do. So, the notion that a new recorder is somehow better than the digital ones being produced ten years ago is flawed. DR2d and Sony M10 rule the stealthy world with long battery life, replaceable batteries and solid proven performance.
New is not necessarily better.
I am confused by your statement. The two recorders you cite do not have digital inputs, so they do not qualify as "bit boxes". They have analog line / mic inputs and preamps, and the quality of those vary greatly across different devices. There have been significant upgrades over the last 10 years in ADC chips as well. I still have my M10, but I don't use it for any serious concert recording anymore even though I still think it is a great device. The new recorders are clearly far better than the older ones, unless you are looking at the cheapest tier (Zoom H1, etc.).
Case in point: Using the same mics, the quality of recording you get from an old Zoom H series recorder is not anywhere even close to what you get from the new F series. The H6 in particular had very noisy preamps, and the F series ones are dead silent, besides much more advanced ADC. Same goes for old and new Tascam: Dr100 mkIII preamps and ADC are much audibly (and measurably) superior to the DR-70D, which I used heavily.
If you use high-quality external preamps, the playing field becomes a bit more level between the old and new recorders. But if you are running mics straight into one box that does it all, the differences between the old and new recorders becomes pretty clear.
EDIT: I should add that I do not have any firsthand experience with "stealth" recording, and I acknowledge I am including much larger devices in my statements.