I do not doubt your skill or experience... so you don't need to worry about that.
I just wish that all fish were treated equally - including Bettas. I would be flamed if I announced that I had a Goldfish in a bowl, but I would be commended if I had a Betta in one. I don't think that's right. I think that all fish deserve at least 5 gallons, no matter if they are 1'' or 2.5'' or 100''. I am well aware of "nano" tanks, "nano" fish and the like. I know how to run one (in saltwater, at least), and I know the increased needs of one.
Perhaps some Bettas are lazy. But every Betta that I have ever had has been far more active and colourful an a tank of 10 gallons as opposed to a tank of <5 gallons. My little brother actually has one in a ten gallon right now, along with a Gourami, Corydoras, and two baby
Polypterus senegalus. He cruises along the entire length of the tank, and his human responsiveness (as opposed to the other fish in the house) is matched only by my Triggerfish.
However, the Bettas I used to keep in fishbowls (years ago) always looked bored, lazy, colourless, and sad. They did blow bubblenests from time to time. When 2 eventually died, I put the last on in a ten gallon community tank (including a female Betta) with a powerful filter and several other sources of aeration (the tank was on the heavy end, stocking wise). He brightened up after a day, and was no longer a lazy creature that lay on the bottom of the tank all day.
Though
your tank does appear quite suitable; plants, good lighting, heating, and a filter if I remeber correctly, not everybody will take this kind of care when setting up a system for a Betta, especially if they have 400000 of them ("Betta Keepers"). And although I do still wish that you had a bigger tank for your Betta, it is mainly the "Betta Keeper" type of people I am trying to change the opinion of.
But basically, I am trying (desperatly, but to apparently little avail) to instill a new idea into fishkeeping. Animal cruelty is occuring when Bettas are thought to live happily in any condition, in my opinion at least. Animal cruelty is a terrible thing, and if the perpetrator is not willing to at least consider an opinion besides their own and give up their self-righteousness, then they deserve to be belittled. I will take care not to be as harsh, though.
I give compliments and many thanks to you for discussing this issue with me, and considering my opinion instead of just being annoyingly self righteous (we both know which users were). You are very respectable in my books for that.
-Lynden