Avoiding the 2HKO from M-Manectric isn't quite as important for this deck as it is for many others because you've got Jagged Saber to heal a Benched mon after you retreat. Increasing the number of spiders increases the chance that you'll actually have one on the field to work with (under your model, if either Spinarak or Ariados is prized, you don't have that option), thus giving you a way to 2HKO M-Manectric with Jagged Saber or Unseen Claw, and Ariados can also soften up opposing Regice for Virizion if you're not behind on Prizes. Jynx, on the other hand, gives you 10HP per turn and does literally nothing else of any value while being massive Lysandre bait and a dead starter (yes, I know, Spinarak and Ariados are Lysandre bait as well, but they have broader utility than Jynx does, and Spinarak isn't a completely dead starter because of that 50% paralysis chance). Jynx is the kind of thing that works better as a one-off tech if it's included, but anything that requires evolving has to be at least 2-2 to be reliable.Jynx is good because denied 2HKO of mega Manectric and it is very important i think.