I also never said that I will answer your questions right away. Just that I will answer all 7 of them once I do reply. The opportunity cost of looking at my email inbox might be way too high at a particular moment and so I might not even see your message for a full day to begin with. Same w/ a slack message. I might not see your particular message for some time or I might see it and decide that it's not a message I can deal with on the side while in a meeting and mark it for later consumption e.g. for when the meeting ends early etc.
FWIW I've so far never seen anyone try to 'use' my thoroughness to create a denial of service attack against me. If that ever did happen, I would definitely change my stance. But it won't be to answer the first question each time. It would be to stop talking to them. Like I ignore any "Hi, can I ask you a question?" messages. Even some directors have tried that and just gotten ignored (first time someone does it, I will let them know they can just ask away. Second time they get ignored until they learn).