.... want to understand how the transition of limit to sustain is going to work in the real world and is going to want to understand the logic behind this sudden block reward drop from the devs.
You keep saying there will be a sudden drop in the block reward as we enter into the sustain phase. All of this is speculation, whereas in reality it depends entirely on decentralized voting.
Although the max vote will certainly drop in the sustain phase (a requirement for assuring the long-term duration of the sustain phase), no one knows whether decentralized voting will have already reduced the block reward during the remainder of the mint phase and limit phase.
It is entirely possible that the block reward vote will already be significantly lower than it is now before we draw near to the sustain phase, in which case there would not be a significant drop. During the limit phase the block reward could be voted down to double digits, in which case there would not be a sudden drop. Similarly it is also possible (again depending on voting) for the mint phase to continue on significantly longer. For example, if miners dropped their vote from 512 to 256, this would double the time until the limit phase.
Finally, whether such a block reward drop (if it would happen) would be good or bad is debatable. Overall, we will not interfere with the decentralized block reward voting. It is completely up to the voting how long the mint phase lasts and how much HVC is mined in the limit phase. That was our promise from the start and we will stick to it.