Nice and thorough guide, only things that I would change is to swap the dash perk for field medic and take T3B instead of T3A on the grappling hook. By taking 3b, you get a slower but more consistent speed boost than dash (which is kind of redundant on scout). With field medic instead of dash you can effectively kite the hoard to one end of the room then zip back and because of field medic you can potentially revive your entire team before the bugs catch up.
Also, an after thought that I had was that when taking Electrifying Reload Deepcore, on haz5 its 1 bullet to kill a grunt so something you could do instead of taking T5C you could take T5A to get a speed boost by shooting a swarmer to get you away if you are being swarmed. Unfortunately, this doesn't work when the enemies die to the electricity. Also, please take my criticism with a grain of salt and really just do whatever is most fun for you.
While I appreciate you giving your thoughts, I would like to note that every point you brought up was discussed in the text part of this karl.gg build. I tried to give context for each build decision so people can make informed adjustments to fit their preferences like the ones you suggest. I know it is a lot of text, but I highly recommend reading through everything!
Bub
For pickaxe power attack I prefer more AoE since packs of grunts tend to stack on you when downed, unless you're fighting bosses like caretaker, so with 1 power swing you can restore much more health than without it
During IW last stand the only goal is to not go back down after it ends. Whether you get 5 health or 20 health with your power attack the same goal is accomplished. I do not think 5-15 extra health from hitting 1-3 more Grunts is enough of a difference to be worth it, especially since not taking the damage mod means a power attack is no longer does enough damage to 1 shot a Slasher or Tri-Jaw. You are going to get most of your health back from resupplies and red sugar anyway.