I think every part of your slow-burn has to mean something. Each point should be exciting to get to on it's own. The difficult part is setting up later plot points. This is especially hard when it comes to character relationships and making them feel real. Unfortunately, I don't have much advice for character relationships without plot-driven forces. Typically I'd just let a relationship naturally evolve parallel to the plot, but if the entire purpose of your story was the relationship itself, I think that's why it's so hard to write a romance novel that isn't cheesy or smutty. It's certainly possible, but it's no easy task.
If character relationships or development are what you're trying to pace, then even reactionary characters should easily thrive as the plot develops. If it's the plot itself that you're worried about pacing correctly, then I'd say that each plot element should be exciting on it's own. Every chapter should exist for a reason, even if it's trivial compared to chapters that reach a climax of some sort. In that case, outlining is your best friend. If you outline by chapter, it should be easy enough to adjust as you go, and it should read as three acts.
I did say 3 acts, but of course you could structure it any way you want, it should just be a clear beginning middle and end, even if you have multiple, or it doesn't have a traditional ending. The red flag would be if your outline is 49% Act 1, 49% Act 3. Maybe that means you're not identifying your own narrative arcs accurately, or maybe it means you created narrative whiplash. Ultimately, there isn't necessarily a right or wrong.
Harry Potter comes to mind. Sure, things happen throughout the books, but typically Act 1 begins with excitement and focuses on vibes, Act 2 usually is mostly setting up Act 3 while focusing on a B-Plot like a quidditch tournament or something, and Act 3 are all the pieces coming together for a climax. It sounds like a typical 3 act structure, and it is, but the amount of time spent on comparatively nothing happening for the first half of the books stands out to the expected climax at the end of every book. I'm bringing it up, because fans don't care. They like seeing Harry and friends go to class, go into town, play quidditch, poke their noses where they don't belong, take tests, bicker and argue. That's not to say that it's everyone's cup of tea, but that good pacing doesn't necessarily require action or even high stakes at every point. It just needs to matter to the reader.
For my main story, I maintain a calendar of events alongside my outline. The calendar is flexible enough to be updated as necessary, and exists for in-universe continuity as well as pacing. The outline started with the most essential events. Then I added in the events that need to happen between those events for it to make sense. Then as I write, sometimes I'll either have a new idea, or realize I didn't leave enough space for certain events. For instance, if a chapter exists because Character A needs to meet Character B for Event C to make sense, but then I realize I only left room for them to interact once, then it's easy to shift everything for a new chapter if necessary. It would follow the rule of chapters existing for a reason. One of my least favorite elements of a story is narrative teleportation. At least in my work, that's something that pacing needs to be planned around. It'd be wasteful to have a chapter just about going to another location, though you could always describe the shifting setting for an entire chapter if you want to, I guess. Instead, that could be a chapter with low-stakes that focuses on character development, something that will naturally pay off later as opposed to forcing it in as needed.
One last analogy, the manga/anime Naruto fumbled the hardest with pacing due to editor pressure. You essentially see them go on one mission, take a promotion exam, and then a blood feud between spiritual brothers. Naruto's great, but in an effort to always up the stakes and progress the plot, they missed out on the character and plot development that could've made future threads even more intense.