Please. If you had "quite an immense experience with fish" then obviously you'd know that one size doesn't fit all and you wouldn't say crap like "I don't believe a lick of that." or maybe you'd just be smart enough to shove your foot in your mouth. :)
I'm betting I have more experience then you but that doesn't mean I value your opinion any less or other people who have bettas successfully in bigger tanks for years, because honestly, I *LIKE* bigger tanks, bettas typically don't[they're not bred to be strong, just sell.] I just don't care for people who wanna treat others who simply state their own opinions like crap. And atleast if you can dish it out, you can take it back.
2 dogs, bearded dragon in 40gB, 4 cats[ugh! xD], 2 turtles[RES/Painted sharing a tank with an oscar & jewel cichlid], 1 temporary 10gal "QT" tank, 55gal planted FW community & 15gal nano-reef ... plus a 20gL planted divided betta tank with 4 bettas that will eventually be rehomed and the tank - decommissioned.