LAMBDA. IS. TAKANO.
Fucking Ryukishi man...
Nah, Lambdadelta was always supposed to reference both Takano and Satoko at the same time. Ryukishi wasn't the least bit subtle about picking traits from both of them when coming up with Lambda.
Just about the only time where Lambda was leaning heavily towards Takano and Takano alone was in Legend of the Golden Witch, where Lambda was just a vague, off-screen person known for her cruelty. Once Lambda actually started making appearances from Turn of the Golden Witch onwards, the Satoko influences became apparent. Ryukishi gave her the Satoko laugh, have her get easily angry when she's mocked or says something dumb, and presents her as a tsundere-type character, which is also how Satoko is referred to in Minagoroshi at some point. Bernkastel even mentions to Beatrice that Lambda gets lonely easily, which references what Rika says to Keiichi about Satoko at the start of Onikakushi.
Of course, she also had traits that fit Takano better, such as her being mentioned as the cruel witch who tormented Bernkastel, so she wasn't wholly Satoko-inspired, and Lambda could've gone in several directions at that point, either becoming more Takano-like, more Satoko-like, or something more original, but Ryukishi liked his super-paper line so much that it ended up as the core of Lambda's characterization, which obviously would fit more with a Satoko-esque personality, and may be the reason why Lambda ended up liking traps and referencing Onikakushi's cake puzzle in Twilight. If Ryukishi stuck with his initial idea of Lambda as a cruel witch, she might've ended up as much more of a Takano-type, instead.
Ryukishi wasn't fully leaning towards one side yet with Lambda, but the seeds towards the almost entirely Satoko-inspired Lambda were already sowed by then. And that's not even considering all the weird parts about Lambda and Bern's histories that don't really match up with anything we saw in Higurashi, such as the claim that Bern defeated Lambda as "a lone piece" (which completely ignores the existence of Hanyuu, who was more important than Rika was in Matsuribayashi), the claim that Lambda "went easy" on Bern and Bern used that to her advantage by putting all her pawns on Lambda's side of the board, as well as Bern saying that she didn't really defeated Lambda so much as she won an endurance contest, with Lambda eventually getting tired and giving up. Honestly, I'm not sure what Ryukishi wanted to achieve with those lines other than fucking with people for the sake of his bullshit "shared universe" nonsense.
More interesting is how Lambda compares to Beatrice, since she describes Beatrice as someone fucking around for her own amusement instead of going for the kill, which I think applies to Takano as she's depicted in Meakashi and Tsumihoroboshi, where she was fucking around with Shion and Rena to no real benefit to herself, which completely screwed her over on at least two occasions, which is very different from how Lambda describes herself, and it doesn't fit the "certainty" concept at all. And while to Rika, Takano represents a certain fate leading to death, Takano never cared about Rika much at all, with her death just being a step in her master plan. Hanyuu is much more of an antagonist to Takano than Rika ever was, what with Takano being so strongly opposed to "god" and her constant rolls of a one that she wanted to overcome by controlling the dice through her own efforts, and Takano actually has multiple confrontations with Hanyuu during Matsuri, while Rika barely interacts with her. None of that really lends itself to Lambda at all.
The weirdest part is that Lambda wasn't even the start of Ryukishi conflating Satoko and Takano as characters; he was doing it for like a year before Umineko even started.
Miotsukushi, which first released around half a year before Legend of the Golden Witch, had a scene in which Satoko empathizes with Takano and describes Takano as a possible future for herself if she lost herself to hatred and despair.
Ryukishi didn't write Miotsukushi himself, so it's unknown if he came up with this idea himself, but he did have frequent discussions with the author, Kanou, and brought up ideas and elements that he didn't end up working into the actual Higurashi product, some of which were then incorporated into Miotsukushi by Kanou. Since this is such a weirdly specific element, I'm inclined to think it originated from Ryukishi himself.
Ryukishi did write the script for Yakusamashi, the DEEN Kai anime arc that was included to introduce some critical plot elements DEEN neglected to include, and was first aired shortly before the release of Legend. There, Satoko ends up in room 3-4 in the hospital, which could be a coincidence, but it's an oddly specific coincidence when you consider that the meaning behind Miyo's name was already firmly established by then.
And when you consider how he continues to link Takano and Satoko together even after Umineko, such as Rose Guns Days' Meryl having Takano's name but taking clear design cues from Satoko, including a dislike of pumpkin, I'm strongly inclined to think that those two early situations were all deliberate. I won't claim to understand why Ryukishi thought this was ever a good idea, but it's clearly an idea he had long before Lambda was properly introduced as a character.
Lambdadelta being revealed as originally being Satoko is dumb, but it's really not the total retcon out of nowhere that people make it out to be. It's hampered by Ryukishi not being a good writer who never managed to shake off that doujin amateur writer impression, but it's clearly something that was conceived of as an idea very early on.