I honestly fail to see what the big deal is. It's an established tradition that in every odd-numbered generation Satoshi fights in the League, goes back to Masara Town, and then starts a new journey (for about a year prior to the following generation) from there. He's just doing the same thing here except in Kanoko Town here, and the lame little girl subplot is to make up for the fact that his thirty or forty someodd Pokemon are not all in Araragi's lab, and therefore we can't have an episode based off Bayleaf trying to hug Satoshi. I enjoy these 'back to the hometown' episodes, as they establish the end of a journey and make us all look back at the past few years as well as being given things to look forward to for the remainder of the generation. I don't really consider them to be 'fillers' at all. Plus, the things like the Mamanbou and the starters are part of the aforementioned way that they're bringing us back to when Best Wishes! first started.
Edit: Also, on the topic (someone, I think it was Silktree, brought it up) of old Pokemon appearing in this saga: I suspect that they will simply provide trainers (Plasma grunts with Golbat and Coil come to mind) with old Pokemon, while leaving the wild Pokemon strictly (or perhaps not-so-strictly) Isshu-only. I can see the wailing already, but let's just compare it to, say, the BF saga, where Houen Pokemon were littered everywhere around Kanto--including many wild Pokemon--and nobody raised a peep. Or, something that always bothered me, the fact that the Rocket-Dan went to fucking South America to find Mew, and yet then we see that there is an area not too far from Nibi City where Mew actually presides and it's not that unknown among the populace there. We have already been handed a similar batch of mishegas with Blacky, who was chosen out of 493 old Pokemon in an early Best Wishes! episode as a Pokemon virtually non-existent in Isshu, yet now we know there's some well-established rescue ranger with his own farm and a plane not too far north who has a Blacky. So the worst of it should be over; expect there to be plenty of trainers casually walking their Maril around the block with no one uttering a peep. Worse yet, expect Virgil to continue to appear in Episode N to promote the Eievui merchandise and walk his Blacky into Don George's training facility in Karakusa Town with no one uttering a word of amazement. On the bright side, this means we will likely be spared having to look at the same few Isshu Pokemon for the remainder of Best Wishes!