Re: Jendon
If Jendon is tapping in a squad that isn't an expensive ace, you really should've spent your points somewhere else. If we price him as though he's always giving an attack to the most expensive ace, then he should always cost the same as the most expensive Imperial squadron. 20 is fine, in my opinion. Giving Maarek another attack (his usual job) is great but once Maarek is dead or out of range if he doesn't have a solid backup option, he's just a Relay 2 node and an extra fairly regular attack. 20 points for "sometimes great, but if you snipe his big friend is not that good" is fine. It's complicated by effects like Squall keeping Jendon bouncing around but that's the fault of FFG for printing Squall in the first place and outside the scope of a squad points change.
Re: Mauler
18 is 2.57 times the cost of a 7 point TIE Fighter squad. Mauler has about the same durability as two TIEs (sometimes less depending on the fate of that scatter token) and if he splashes for 2-3 damage once then he's doing about the same total damage as two TIE Fighters but in a one-squad package. He can get nuts with multiple hops but Tien Numb can get nuts with multiple splashes too. I worried that at 19-20 he'd just be too pricey. It's basically on the Mauler player to find a way to splash more than once or for more than 2-3. It's on his opponent to try to stop that. Assuming he's used in a fairly average way, 18 feels like a fine compromise but I'm not opposed to more. It just feels like maybe too much.
Re: Vader
I'd give him serious consideration at 19. He's an absolute beast against squads (seriously one of the best anti-squad aces in the game, hands down), especially with Flight Controllers. He's fine against ships (average of 1 damage due to the crits counting as damage, although he's not a Bomber). It's just Escort lets him down is all.
On a side note, if it was up to me I'd remove every automatic-damage and out-of-activation movement effect from the game and replace them with something else as they create difficult-to-balance effects but that's outside the scope of the mental exercise.