Digital Leica M bodies have never reigned over the competition when it came to specs. But it's also comparing apples to oranges. If you need DSLR features, get a DSLR. If you need a digital rangefinder - there's only one option, really. In the end, it's all about the rangefinder experience (simplicity) rather than pure specs.
Of course the Leica M can't do everything nor should they try to. Again, that's the rangefinder part of the equation. Different tools for different jobs, and why I picked up a Fujifilm X-T1 - for when I need DSLR-like features (e.g. zooms).
Dust removal is nice, but overrated. Won't help you at all with "wet" spots (e.g. oil). Cleaning a sensor is no big deal. I can count on one hand how many times I've actually had to clean my digital M sensors in six years. Heck, I cleaned the Canon a lot, lot more in half that time.
As for the other digital cameras in Leica's stable, well... I'd blame Panasonic more.
The T is Leica's hope for a breakaway product. It's certainly a technological shift for Leica, and even most other digital compacts. Feature-wise it's not super loaded, but everything else about it is. The beauty of a highly software-centric camera is that you can update the firmware, gaining new features, changing old ones and fixing bugs. Give it time.