Here's my take on this:
Even though Arc's air throw has increased recovery in AA compared to AC, it's not totally a bad thing to use sometimes. However, she does have other options that she can use to setup an untechable knockdown. For example in the corner with C-Arc when you do her b&b wall slam loop you can end it with after 2C (delayed 4C, AD j.C, land 5A, 5B, 2B, 2C to 623A or delayed 236A, 236A, 214A). Either the 623A or 236 rekka finishers will setup nicely to any decent oki option (IAD j.C, 5[ B ], 236[A], etc) as opposed to air throw. If you land a wall slam throw near the corner, your only options of course would be air combo to air throw or j.2C for tech punish setup, but if you really want to and you have ample meter you can do 22A after throw then land and juggle with 623C to oki setup (make sure you do the reversed command 421C after 22A in the corner since the game thinks you are landing on the opposite side of the opponent).
As far as mid-screen goes the ideal option would be to combo into 2C then do 5C, homing jump to j.B, j.C land to wall slam loop, but depending the opponent's character and your positioning towards the corner you may not always be able to land this setup so most players will take the simple route and do air combo to air throw instead. The trade-off with doing air throw of course is that Arc bounces away from the opponent after she lands and with the increased recovery from air throw you pretty much barely have any time to run back towards the opponent so they can easily run away from you which ends your offensive advantage and resets the situation.
Arc really didn't need to have MORE recovery on her air throw but they decided to put it in there anyways so I guess we'll just have to deal with it.