But then I looked a bit deeper and realized that there did not seem to be any real alternatives to Starbucks - for the type of sit-down-for-hours place I was looking for.
So, 'real' in this case means a place with nice, comfortable furniture and an atmosphere that says, "Welcome - stay a while." -- i.e. a real third place.
When I check out Caribou Coffee, for instance, which may be the biggest somewhat-like-Starbucks coffee chain in the US, and it's eh -- I really don't even want to go in. In terms of potential work space welcome, I'd give Starbucks a 6 or 7 and Caribou a 2 or 3. Why? The cheaper, less-comfortable-seeming furniture, seemingly-smaller/tighter footprints, etc. -- the whole vibe is more fast food than I'd prefer.
A place like Panera Bread is interesting-ish, but doesn't quite feel right - like when the lunch rush comes, you feel in the way -- because you probably _are_ in the way -- they do things like set timers on the wifi, etc.
I do have some smaller cafes that I go to -- some might even qualify as small chains (e.g., Dancing Goats) -- but I was kind of surprised to find out that there are no very direct Starbucks competitors for a 'third place' in the US.
Maybe places like Caribou or Philz or whatever will just take 10 more years to try to grab some market share? Or maybe Starbucks has already reached an Amazon-level of super-dominance that can now never really be challenged.