Whatever Samsung is doing, it gained them market leadership, so they're entirely justified in doing the same thing over and over again with minimal changes. HTC is not in that situation.
But Samsung has only ever done the same thing with each of their smartphones. All of the Galaxy S updates were small and evolutionary, same with all of the Note updates. The biggest update to any of their smartphones came with the Note Edge and that was only after four years of having the Note released. So why can't HTC do the same thing? In fact, every smartphone manufacturer has done the same thing. Each update is not intended for people to get new phones every year especially when most people are on two year contracts and get new phones only when those contracts are up. No, smartphone updates now are for people to upgrade every other year. You will only ever see small updates when upgrading every year. Compare the S4 to the S5, there wasn't much of a difference in performance, camera quality, or anything else. Compare the S3 to the S5. Well yeah, that was a big leap in performance, battery life, camera quality, display quality, etc. Compare the M8 to the M9. It's not much. Compare the M7 to the M9. Again, there will be major leaps and bounds in performance (especially for 64-bit optimized apps).
I'm not sure why you are hammering HTC for making an evolutionary update when every company (Samsung, Apple, LG, Google, Motorola, etc.) has only ever done that between each annual release. HTC's sales numbers may have decreased but that doesn't make them dead. They are still above and beyond BlackBerry. Even if HTC were to dramatically re-design the M9, I doubt it would make much of a difference. People are so caught up with brands now that they are either Apple or Samsung. Very few people know about HTC, Motorola (which used to be a household name), Sony BlackBerry, Microsoft, and Nexus phones. That doesn't mean that those other companies make bad products, far from it. They can still be successful in their own right without taking down Samsung or Apple.
HTC's goal at this point is to sell more phones, not sell more phones than Samsung. They could easily do that with the leaked M9 design especially if all of the issues with the M8's design have been fixed.