No, actually it's not 'good' that they're doing this based on client count.
#1: This will cost them money in the longrun. If they did things properly (a flat out , across the board raise), this would make them money.
#2: They offer nothing additional at all. Nothing.
So, a client with 1 client gets the same, exact service as a client with 1500, yet that client with 1500 clients gets charged almost 3x as much, simply because 'tax'.
That's essentially what this is a 'tax' system. It's horrific to say the least. There's no justification for it, except because they're WHMCS.
These people don't contact WHMCS more (in fact, honestly, it's the other way around), they don't require more support, they don't get much anything different from WHMCS... So, why, again should they be forced to pay more?