That's what I mean though like... right now we're doing much more and more coherent planning than ever before. It's actually lack of planning which makes it easy to switch things around.
As I mentioned at the start, Unwelcome Guests wasn't intended to be a "quest" in the sense that anyone would think to count it towards the total number of quests released. As it happens, the team did a great job and shipped a "miniquest" to which players responded "this is a perfectly good quest, it should be a quest and give a quest point".
We agreed and responded to that feedback by adding a quest point, and now Unwelcome Guests "counts". If we had arranged an elaborate schedule to make sure that a certain quest launched as 250, we would have had to say "no, sorry, we're not adding a quest point to Unwelcome Guests because it will throw our completely arbitrary numbers off" or tell the devs "make sure you don't put too much effort into your miniquest, we definitely don't want the players confusing it for a quest". IMO both of those would be bad for the game, but when you say "plan better" that's the sort of thing that would have to happen.
Right now we're getting to launch more frequent story content than we have for a long time by being a bit laid back about it - the devs are being asked to include some story with their updates, but we're not being strict about whether it is or isn't strictly speaking a "quest" and we're not setting minimums for length, quality, etc. (Obviously this is different for the headline quest months like Murder on the Border, but for the skilling and combat focused updates.) That gives the team the freedom to do what they can with the time available, and the results so far have been surprisingly good. According to the schedule, we have only shipped 1 quest this year so far, but we've actually got "more quest content" than that and IMO that's much better for quests and the game than trying to line up some specific quest with some specific number.
The other obvious elephant in the room is that the only reason we're anywhere near 250 is because we recently reclassified some other miniquests and non-quests as quests. We could undo that, or we could classify a bunch more as quests and overshoot. Again I don't think that whether a miniquest is classed as a quest should be decided based on whether it interferes with a milestone - that would basically be making design decisions not based on whether they're right for the game, but whether they're good for marketing. I'm kinda surprised to see players advocating for that.