I had to go away and think about it because my brain went blank on series where I either liked the protagonist best, or at least felt like it was conceivable somebody could.
Blank slate protagonists do have a purpose, usually it's either to make the story feel very immediate and allow the reader to put themselves into the Fantasy (blank slate like Bella Swan who is meant to be a blank that a teenage girl could insert herself into), or it's because the plot is the main star of the show, and the protagonist is more like a viewpoint (Garviel Loken in the Warhammer Horus Heresy books is a pretty bland character with very little impact on the narrative, because he's more like a viewpoint for the reader so they can see all this epic sci-fi lore unfold on a more human level). A lot of videogame protagonists lean a bit blank slate-ish for obvious reasons.
Then on the other hand, you get a story where the character's journey, and the changes they go through are key. Anime are often pretty good for this. Spike from Cowboy Beebop, for example, or Ed Elric from Fullmetal Alchemist. Some series inspired by anime, like The Owl House or Avatar the Last Airbender, also have interesting protagonists in Luz and Aang. These characters aren't just intended to be a viewpoint to experience the story through; they ARE the story. The story is shaped by these characters' decisions, especially their bad decisions.
Making a character with a strong personality is always a risk because people in the audience might not like them. Like Shinji from Evangelion. He's technically an amazing protagonist, with deep ties to the plot, a very distinctive personality and character development throughout the series.... and some people really don't like him. They're like "UGH he's so whiny! He's such a loser!" It can be hard to strike that balance where a character is flawed enough to be interesting, but also cool enough that somebody would want to see themselves in that person.
So when I was planning Errant, I'd decided Rekki was going to be really quite a flawed character with a strong personality who makes some bad or frustrating decisions, and I did worry it would cause problems. It's always a bit of a relief when people vote Rekki as their favourite and say she's relatable! A big factor with Rekki was establishing why she's like this, and showing why she's a worthy person in spite of all that. I ended up starting with a prologue rather than my original plan to start with adult Rekki and then later flash back to the events of the prologue, because it felt important to show the audience though presenting her as a guileless child, that fundamentally, Rekki Lune is a brash, heroic person who'll throw herself into danger to protect others in a heartbeat... and also that she has a lot of deep-rooted insecurities about not being good enough, and that the villain, Urien, uses those insecurities to manipulate her. As the story progresses, we see more clues emerge that she's kind of chosen to take on a lot of burdens in secret, both out of necessity, to keep the villain out of the loop, but also as a kind of self-punishment. That was the part I knew was going to be tricky, because early on it's deliberately ambiguous how responsible Rekki is for the bad stuff that's happened, and whether she's genuinely protecting that status quo, to create narrative tension. There's no internal monologue or thought bubbles in Errant, so I had to put a lot of trust in readers that they'd want to wait it out and see as more is revealed!
It'd be arrogant to say I think Rekki is a "great protafonist", but one thing I'll say is that I did make an attempt to risk making a complex, flawed protagonist who won't necessarily be somebody the reader wants to see themselves in, and I think that can be what's involved in making a great protagonist... but whether somebody things I succeeded or not is really more up to them! 
