I strongly disagree. I don't think it's true at all that Ridley ever "split" the vote with Dark Samus to any degree. Ridley was always THE one, THE choice of the Metroid fanbase by far, even as Ridley fans were beaten down by Sakurai and other Smash fans' words. The story of Ridley is a story of a fanbase's resilience -- a pizza that wouldn't cook no matter how much the chef yelled. A toilet that wouldn't flush no matter how much the plumber plunged.
Ridley was overtaken by K. Rool in the ballot -- and many other characters -- but Ridley still held on. Dark Samus was always a far off dream.
Dark Samus got her butt kicked by Dixie Kong in the ballot. You can look up the polls from that period and Dark Samus doesn't even register. Dixie does, even if notably below K. Rool. That still put her ahead of a lot of characters, including Dark Samus. In fact, the furor over K. Rool helped Dixie relative to other characters because it kept her around in people's minds. She was often floated as a "realistic" alternative to K. Rool. The conflict fed the Dixie machine.
Oh trust me, I know. I've been waving Ridley's flag ever since the Melee intro 18 years ago and I was actually moved to tears by his reveal trailer. But I think people forget how battered the Ridley fandom was after Smash 4. It was pretty clear that the whole Pyrosphere shadow situation took the wind out of their sails. I still remember the very somber sign-off thread on Smashboards after his disconfirmation with a number of people saying it was their last rodeo because they were exhausted after how much of a rollercoaster the whole Pyrosphere situation ended up being.
The ballot was just rubbing salt in the wound because everyone correctly assumed that an existing notable role in the game was a damning mark against them. As someone who frequented a lot of Ridley threads across the net, I saw plenty of people saying that they were going to move on to Dark Samus or at least throw her a vote alongside Ridley. That plus the fact that Sakurai outright said Dark Samus and Chrom were added to the game for popularity reasons has me thinking that, ironically, Ridley's deconfirmation for Smash 4 resulted in us getting an additional Metroid character in the end.
As for the Dixie situation, yes, she was presented as the realistic alternative to K. Rool, but that was mostly before the full game released, and certainly before the ballot came up. Because of Tropical Freeze being recent and no one knowing when the cutoff was at the time, most figured Dixie had a great shot due to recency whereas old Mario Sluggers-only K. Rool was constantly given the "irrelevant" brush-off. Once the ballot appeared and the idea of a character getting into Smash on popularity alone became a feasible concept, the K. Rool squad went into overdrive with the Kremling Kampaign and left Dixie in the dust.
As for the fan polls, I'll admit that Dixie did chart better on those than Dark Samus, but as I mentioned earlier, many of the Metroid fans had lost hope and probably moved on from where the polls were happening. After all, Ridley himself didn't chart on a lot of these polls. I just think you're underselling Dark Samus's (confirmed) popularity and overselling Dixie's at the time. She's definitely going to become an enormous force now that K. Rool's in, but it's a similar situation to the competition between Diddy and K. Rool in Brawl: one only really takes off after the other is already in.