Both as a reader and for curatorial reasons, my own personal preference is to treat the artist's presentation the work as authoritative.
If the artist has divided a (longish) work with chapter numbers under the same title, I would generally prefer to honor that using the chaptered approach. This is reasonable as the the artist's organization often presents a sensible compartmentalizing of the story into more digestible chunks, and sometimes signals a shift in story or perspective within the same universe. Multiple chapters can be linked to one another in the pool description; this allows for ease of reading in installments, with a minimal 2-click overhead to advance between chapters. Thus, I feel the current handling of A Bright Future, Spun Yarn; and having Scarlet Devil School distinct from Four Seasons' House, are appropriate.
forum #62915 raises the question of pool #2104 where continuity is present, but the artist uses a different title with numbering restarted. I consider this analogous to division into chapters by the artist, and would begin a new pool for the new title, with appropriate linking. (In fact, this is already the case for the series prequel.)
This does not repudiate lumping, however. Flexibility is needed in the case of much shorter works; as F.I.A notes, if each of the chapters has only a small handful of posts, then the chaptered approach confers little benefit and the lumped approach may be more appropriate. e.g. YamaKisu and Danbooru House Minoriko are collections of variations on the same short gag. By that argument, Butt knife 1 & 2 could be lumped together as well.
Mamange kind of falls into a gray area here, with short to medium chapter length varying between <10 and >20 pages, but having over 150 pages in total. I might have chaptered it if I were the pool creator, but I am also perfectly happy with how it is currently organized since it is not prohibitively huge.
As for sequentially ordered/numbered comics that the artist has not divided into chapters, I consider it desirable to preserve the artist's ordering and consume the work in that order, even if the pool title is generic and corresponds to a tag search such as "artist_name touhou 4koma". This is regardless of continuity or lack thereof -- it doesn't matter whether the comics are completely independent one-offs, a single continuous story, multiple shorter threads, or a mix.
I agree that if a series contains shorter, minimally-related story threads within the whole, it would be convenient to be able to easily find and access those. But, I would consider it presumptive for us to arbitrarily split the work into "chapters" if the artist did not do so; indeed, some works do not exhibit clear boundaries for splitting. Therefore, I would generally prefer a single pool, using a table of contents to link to the start and end of any sub-story threads. E.g. in rokugatsu's 4koma pool, we could have a link for the Young Ran Adult Chen thread given as: strips #14 ~ #20. Nesting pools such as pool #2502 is undesirable since it increases the clutter of pool headings above the image and does not add any new information about ordering.
Notice that in general, the artist's series organization and story continuity are not mutually exclusive nor do they contradict one another:
- If there is little or no continuity, but the artist has provided an ordering of the series, the ordering is still information that some people care about, and can and should be preserved as an ordered pool without detriment to (inexistent) continuity.
- Where the artist has provided an ordering but it consists of fragmented, independent story threads, then the continuity is contained within the artist's ordering. We can preserve the organization (which some people care about) as a single ordered pool, while still linking to sub-story arcs of interest within the whole to indicate the distinct threads.
- Where there is continuity, and the artist has divided the work into substantively sized chunks by chapters or otherwise, we can and should preserve the artist's organization, it often represents sensible splitting points and/or perspective changes. Continuity of the whole can be accomplished by linking between pools.
- If the individual chapters are too small then they can be lumped together at discretion.
Of course, if the artist did not number comics as a series or organize them into chapters, then all bets are off. Story threads can be collected using pools as deemed appropriate.
Since series continuity really is a continuum rather than a binary classification, I don't think there can really be a strict one-size-fits-all policy in this matter. I am fairly satisfied with the status quo, but a few pools like pool #738 could really use some cleanup. We could establish some general guidelines if that helps to clarify things. And as always, a healthy dose of common sense is beneficial.