Regarding armor, I really dislike the new rules for several reasons. (However, just to be upfront, I don't have any real suggestions, primarily because I just don't understand what was wrong with what we had, possibly because I haven't done a lot of vehicular combat, and when I have I've exercised a lot of what I consider to be common sense.)
First, as many people have observed, the extreme compression of armor values is basically nonsensical, both in equipment and in xenomorphs.
Second, there's just no room in the current system for destruction by acid splash, which -- while minor -- is such a stressful, evocative, part of ALIEN lore.
Third, my tables have always enjoyed armor rolls. I don't get why these tense, exciting rolls were removed.
Regarding injury, my group likes the original table. (Admittedly, if a given injury seemed impossible to explain in the context of what happened, we'd roll again.)
In a game that uses so many tables -- but also has such clear, easy-to-read, understandable tables -- why not just have a few different critical hit (or serious injury, or whatever) tables? Non-lethal, bludgeoning, puncturing, severing, just off the top of my head. The table can be referenced (e.g., in xenomorph signature attacks) and/or it can be a matter of GM's discretion.
(I also advocate strongly for separate stress/panic tables for different activities. When it comes to an RPG, tables are just about the best and fastest way to reference information. Why not lean into ALIEN's use of them?)