While I still dislike too-large numbers of viewpoint characters, I’ve come to the conclusion that they’re more a symptom than a cause of questionable writing by themselves. I say this because I’ve read a lot of good books that have their share of them.
Now, this could be just the stories themselves being good enough that I can brush past the viewpoint character issues. But I think the bigger issue isn’t too many viewpoint characters per se so much as too many environments. Team Yankee was able to flow well despite having, on-paper, a lot of viewpoint characters, simply because almost all the action was in the same general environment. It adds a sense of connection, a feeling of purpose, rather than just being a clunky “this happened here, then this happened here, and then this happened here…”
It’s obviously not hard and fast, and all boils down to that intangible writing art. It’s possible to have a bunch of environments that works better, and it’s also too possible to have a one-environment story that still ends up as clunky and dubious. I’d still recommend trimming the viewpoint characters, simply because it’s an easy solution, but I think they’re symptomatic of just too many environments and plotlines.