It just looks like this list is being evaluated in a vacuum, which makes no sense given this is a team based game. You say Deande is no game changer like Alani, but given Deande has really, really good assassination tools, she can burst the same game changing Alani in a short amount of time with the Alani not knowing what’s happening until she’s almost dead. Any well played assassin can target 3/4 of the S tier and scare them off/kill them, while avoiding the fourth.
Before we decide why they’re only two steps apart, we need to determine what each tier means, and the discrepancy in power between them all. In my experience from fighting games (Including team based ones), S tier means you need to know everything about that character, know how to play against them since they are going to be picked the overwhelmingly vast majority of the time, and be prepared to play them at any time. D tier typically means almost unplayable/Dead on Arrival, especially when an S tier exists. S tier means 0 weaknesses (Old Galilea and Ambra) and D tier means no matter how hard to try, mastering that character will only lead to failure against someone semi-competent with an S tier, and that disparity does not exist in this game.
We all need to be on the same page as what ranking means what and why before we can formulate lists. That’s why + and - will be in many tier lists, since differences in power can be so minimal, but still do exist and must be acknowledged.