Very true. And please don't get me wrong: I'm looking forward to a traditional and expansive version of SW storytelling since that's what I'm a big fan of (I'm as hyped for Thrawn as anyone). But I do get where someone like Sassafras is coming from. If someone was enjoying the limited and more personal scope of the loner gunslinger with a baby to deliver to safety, then getting full-blown live-action Rebels now would be a letdown.
You're right that there's no way to know for sure what the long-range plans were, but it's not like Favreau didn't go on record several times in 2019 describing how isolated the show would be from other SW storylines. Making this more of a Rebels sequel going forward wouldn't exactly jibe with that premise, imo.
It's obvious that Boba Fett was set up in Season 1. It's also obvious that the darksaber was set up in Season 1. But those elements are still directly associated with Mandalorians. There's a clear connective tissue there to Din and his origin story. But now, I think we can expect Ezra and other Jedi-related branches to the story.
I remember a discussion here (probably this very thread) prior to the debut of the first episode of the show. I wondered whether a series about a bounty hunter, without the Force and Jedi involved, would still feel like SW. The responses I got were that it was going to be refreshing to focus exclusively on scum and villainy while giving a rest to the Force and the Jedi.
Well, aside from Favreau's comments on "new characters" etc. if you tell me this show is set in the Outer Rim, based on Western serials and samurai films, I'm gonna think more along the lines of the old Kung Fu series, or Rogue One...
And for a while, it was so. Even Kuiil describes the Child's abilities as "something he had heard of".
I had no doubt that the road would lead to Luke. EVENTUALLY. Not, necessarily that the Child is even left with him. Maybe by that time Grogu would have made the decision he doesn't wanna be a Jedi - since Filoni opened that door. You don't HAVE to be a Jedi just because you can wield the Force.
I sure didn't think Ahsoka would show up at all, since in theory she was BUSY elsewhere. To me this feels like Disney called a meeting, KK's eyes blazing red with greed and potential license deals, and said "how about this?" All of a sudden it's not serial Western samurai grittiness with quirky offbeat characters, it's kid friendly heir-to-the-throne (because everyone loves kings and princes and all that) and too-good-to-be-real Ahsoka Tano.
And I'll guess the real truth will never be known, tho to me the direction change smells of overstuffed commercializing, not serving the original narrative. And suspect Favreau is an old hand at the film/TV financing game e.g. you give to get. And as Gallery 2 said, the Volume is even bigger now.
As said previously I'm hoping any Rebels related stuff is told primarily in the Ahsoka show, but if there is an overarching narrative that leads to a crossover "event" or two I'm OK with that provided it doesn't replace Din's main story. IMO most people knew the show's story had to expand beyond the Mando & Baby Yoda Show in order to sustain itself. I mean, once he's tasked with returning Grogu to the Jedi it was pretty obvious (as Khev indicated) that the road eventually led to Luke, and I also think if Mando took much longer completing the task we would quickly lose patience and start joking about his competence. We're not exactly a forgiving bunch, we SW fans.
As this is called The Mandalorian, now with that task complete his becoming embroiled in the fate of his adopted home world & coming to terms with his upbringing/beliefs seems like a natural next step. Hopefully he eventually gets to reunite with Grogu and gets to go shack up with the widow from Season 1, but in the meantime I say let him go play hide the Darksaber with Bo-Katan and Koska Reeves.
. Like when I couldn't figure out why DC had gone so far off the tracks and then started reading about who was in charge. 
