When you proposed having filler in lieu of resolving the plot at the beginning of the fic. That would be the point you're trying to argue against, after all. As in, I'm saying that if you have a Point A (i.e., the plot at the beginning), you'd better be prepared to follow through and continue forward towards Point B. Having anything between those two points that wanders away from getting the plot at Point A resolved will feel like you have an unresolved plot. I'm not sure how much clearer I can make that if there was an issue in coherency there.
If it helps at all, think of it like this. You proposed that in order to make a starter ceremony feel less generic, something should happen. Let's say it's Team Plasma stealing a starter. Then, even if the starter is recovered, the reader is going to expect more about Team Plasma because, let's face it, early encounter means it'll probably be in the trainer's mind because that sort of screwed up their starter ceremony. However, you also proposed having subplots in between a section that starts off the main plot and the rest of the main plot. In this case, it would be that we don't hear from Team Plasma until the first or second city. Your readers will wonder, then, why we should care about the trainer capturing a Patrat or getting character development when the main point of the fic has suddenly, in their minds, become all about Team Plasma and the character's fight against them. Even if you didn't mean to have it be about Team Plasma, it suddenly is on a level because your readers will think huge event at the beginning revolving around them = clearly, nothing else matters. That means that, because a fanfic is a lot like a novel, events that happen thereafter will in some way be related to the character's fight against Team Plasma. (See Ultimatum for an example. Farla's Lucki is another example.) That's because every word that goes into a fic needs to lend itself to an overall meaning. Going off on tangents (like the ones filler chapters present) will just make it feel like you don't have a particular focus.
This isn't to say that there's no such thing as a filler chapter in fanfic. However, even in filler chapters, there's always a thread of any unresolved plots in those chapters as well. I'd hate to bring up an egotistical example, but in my own fic, there's a number of chapters where the most important thing might be a conversation between the two main characters. Even so, there's always something important that's brought up in that conversation that eventually goes back to the main plot. So, no time is really wasted because everything links back to the main plot in some way, and it's clear to a reader that this is true. Moreover, these kinds of chapters don't happen until much later in the fic; the first several chapters are directly related to moving the plot forward in order to reassure the reader that, yes, there is a plot. You seem, as far as I can tell, to be proposing true filler, in which nothing directly related to the plot happens. That's unfortunately not how fanfiction works because of the whole "needs to hook a reader" problem.
I knew that already. To help out, here's the quote again.
Note that I'm saying that people are upset with the absence of those two episodes because they resolve a plot point. I never said anything about those episodes being banned because they resolved a plot issue. Why would an episode be banned because it resolves a plot issue? :/
Moreover, to go back to the main point, I'm saying that if you have filler that early, it'll feel like you're dropping the plot in favor of something else. Moreover, if you do have any subplot in a fic, it should be resolved, or you should write it in a way that makes the reader feel like it's eventually going to be resolved. In other words, the main issue is the delivery, but either way, the beginning of a fic is no place for filler because it sends the wrong message (that message being "this writer can't focus on an important plot long enough to follow through on it") to a reader.
