If you were to remove Vegeta from the Freza Saga Equation, I see two possible outcomes.
1. The Genyu body switch happens like normal, Genyu wins.
2.The Genyu switch doesn't happen(they might well not even show up if not for Vegeta murdering al of Freza's men early on), Goku never gets the resulting near death experience and power up, Freeza absolutely dominates Goku.
This is also assuming, of course, that there was no way Freeza was ever going to get the password out of the Namekians.
It's really hard to say though because Vegeta was a
hugely active character in the Freeza saga and removing him changes a ton of variables.
Ryo came in well before she ever got the biomerge, and I felt she didn't really improve that much till after he came in. He wasn't a great character, but she was no less awful. It was nice that it was believable with how long it took for her to mature, but it didn't make her less ridiculous overall. I honestly never really liked her as a character, as even as pretty much a Sue(it doesn't matter that Ryo did it worse), she was beyond cold-hearted. No digidestined(that was that way right away or at least wasn't being controlled/directly corrupted) was ever that horrible. I severely disliked her period. Ryo I didn't like either, but he had nothing interesting about him to go off of to like.
You can dislike or hate Rika as much as you want, but Mary Sue? She's deeply and blatantly flawed, she has a character arc, she stays in charcter for the entire series(minus the Locomon movie), she suffers lots of troubles, setbacks and embarrassing moments, she's not comparatively more useful than her co-stars once they gets in the swing of things like a couple episodes in(in fact she spends most of the series behind the curve), the other characters don't treat her like she's perfect(especially Henry) and while her struggles are played sympathetically the show is very critical of her and never lets her have a pity parade. And she's quite realistic, I've definitely meet real people a LOT like her, and yes, even some her age. I would never even consider calling her character a Mary Sue. Maybe a deconstruction of Mary Sues that gets to the deconstructing very, very fast.
As far as no other digidestined being like her...Christopher? Unless you're being semantic about in which seasons they are technically called digidestined or not. I also don't see why having a "horrible" digidestined is necessarily a bad thing, especially in a season that is decidedly way darker than the other seasons and in which character flaws are basically the central focus of the entire season.
Just me personally she's possibly my all time favorite digidestined. Either her or Henry. Those two are WAY ahead of all the others for me (which is not to say I don't like the other digidestined. I like almost all of them).
