I agree for the most part with your analysis of the reactionary errata to both Hot Lead Flyin' (HLF) and Paralysis Mark (PM).
But I also agree with a general consensus that Negative Play Experiences (NPEs) both 1) exist and 2) are bad for the game.
This begs the question: What is a NPE? I can attempt to offer a three-fold answer to this question.
The way I see it, there is a fine line between losing by being out-played and/or out-lucked, and a full-on NPE. To me, without doing all the complicated maths, the best way to informally measure this would be to look at the ratio of cards like HLF and PM drawn in a single game to the probable win percentage of the person who drew them, all other things (deck build, pilot skill, sheer luck) being treated as equal. And, what pushed those cards for me into NPE-territory is the strong correlation between drawing those cards and winning matches, having a minimizing effect on all the other factors in a given match-up (build, skill, luck).
Secondly, these two cards, by virtue of the "shadow" they cast over the board, violated a fundamental design axiom of Doomtown Reloaded as it differentiated itself from Classic: Incentivizing Interactivity through the Townsquare. Each card did this in it's own way. Decks that both packed 4x HLF and camped the Townsquare created a damned-if-you-do-damned-if-you-don't situation where with minimal build-up, if you were playing against a HLF-camper, your options were to either charge in and "win" the shootout (and likely lose your whole posse), play "around" the Townsquare (with movement and positioning heavily leveraged against you), or to fight fire with fire (also play a HLF-camper). In a word, this deck dictated game state, and made it so if you wanted to have tools to fight against it, you had to build and play completely around a single archetype in hopes for a modicum of a chance.
With PM, a similar situation occurred.
Finally, there is the ability of the game to attract new players - more players means the game deepens and it's run improves in longevity - and both deck archetypes were, simply put, unfun for new people to play against. The following questions might come up: "If this game claims to use poker to resolve conflict, how come one card completely bypasses this aspect of the game?" and "If this game claims an intense chess match to close out, how come one card completely bypasses this aspect of the game?" - something a more seasoned player may be able to play around, but certainly a considerable obstacle as concerns growing the general player base. Suffice it to say, there is a difference between bending the fundamental structures of the game, and breaking them altogether.
One tool the developers used to gauge how powerful cards were was the turnout in tournaments: If the decks in the top spots have a spread of diverse archetypes, the game is doing good - If the decks in the top spot consist of only one or two archetypes, something needs to be done.
Was it an overreaction? Yes (in my opinion). Was it necessary to do something? Yes as well. So. Here we are.
I for one am excited that in the changing of hands of the game's development that these issues will be looked at again from a fresh perspective. And you gotta hand it to a team of developers who reach out to the INTERNET for feedback. Even if I will also say that the Doomtown community is a pretty solid and respectful bunch, all in all.