Even with AK 25 (which Alts won't be capable of getting higher than 15/20 via catch up) it would still take so much grinding that 99 would have no life and it'd still take more than a Year of non-stop grinding to even get to 54. Rank 35-54 does NOT effect iPvP in any way, according to a Blue a while back, so your argument about OP Twinks doesn't really hold up. WPvP and PvE Rank 54 is only a 15% benefit from Rank 34.
Also, to say it's only AK stopping Blizz from allowing 98+ from having access to the catch up, then why even allow 98+ the Artifact Weapon at all. They clearly intended 98+ to be capable of completing all the Quests, do some Dungeons, have an Artifact Weapon and increase it's Rank, I see no reason why to continue gimping it. At first, and for the first Raid Tier sure, after the 110's are 900+ iLvL there's no reason whatsoever not to allow Alts to have an easier time playing catch up.