Uhm, your math is a little off regarding the number of accounts and passive training.
Underlines are what I added.
"1 normal account = 1 character with passive training and 2 more without
1 VIP account = 3 characters with passive training"
"If the intention is to have maximum one character per account on a single campaign, isn't that a disadvantage for VIP accounts?"
No. A VIP account is better than a Standard account. Now the player/person who does this will have an "advantage" over the person who just gets VIP. (And kindly supports ACE)
You are trying to compare 3 accounts to 1. Of course 3 accounts are going to have an "advantage" over 1.
This is in the same way that a guild's worth of accounts (~12 to 200?) is better than, or has an "advantage" over 1.
3 normal accounts = 3 characters with passive training (forever) on the same campaign and 6 more without passive on different campaign = 90$ on KS (+1 month VIP each), equal to ~4 VIP months
1 VIP account = 1 character with passive training on a single campaign and 2 more characters with passive training on different campaigns
3 normal = 3 chars with passive training forever and 6 more without passive training = 150$ equal to 9 months of VIP membership"
In regards to the last part the point of locking access is so that one account which has access to the same EK and probably bank, is not going to have the same account's characters importing ridiculous amounts of materials, resources, equipment, or high level/stats characters.
If you treat each account as if it were a separate player, then yeah it's fine. Even if you treat it as one player like in your scenario, it is once again analogous to comparing a guild to one player. This is because if you treat multiple accounts as one player, it's as if you have a guild leader ordering around his underlings what to do. It's as if he controls not 3 but 12, 20, 50, 200+ accounts! What's even better is that these accounts that you will partially "own" (or can call aid from if you are just a member) is that they are autonomous! They still level up and get kills without any intervention. I call it passive playing. "Join our guild now and get access to 20 passive playing accounts! All for the tasty price of NOTHING"
So, now my question is why not join a guild, get one account, and use teamwork instead of trying to exploit everything for yourself for something that effectively makes you 3 players.
TL;DR You are trying to compare 3 accounts to 1. Of course the 3 accounts have an advantage, in the same way that a guild's worth of accounts has an advantage over 1. The comparison is trivial.