I'm against the grain on this one, respectfully to those with other opinions though.
Today's bettas are often prone to health issues as it is, especially bad finnage, majority are mass bred and genetic health isn't cared for much these days with them. They tend to be more prone to problems and keeping them in conditions that increase those odds of problems I find is more risky than it's worth. Nipped fins from them bickering are likely to get infected easier and other stress-induced illnesses can happen as well. Plus, most are gluttons so can easily overeat, which can risk bloat and dropsy. Group settings and community setups are much more difficult--though not impossible--to manage this over eating habit. I've not had success with them in communities as they'd either be terrors to tankmates or would gorge themselves to death, regardless if I fed at night to avoid them eating too much... they'd still find the cories or such eating their wafers and they'd gorge themselves off that

i find it's better for the betta to have a more controlled environment by itself.
How they'd fare in a much larger tank, that's an interesting concept, but try convincing most of this hobby what's a large enough space for even one betta, let alone a group. Juveniles who grew up together may do fine, but a lot of people try to insist long term sororities with too many adult females for it to stay successful. There is a general low success rate in longterm group setups, as a whole. Fish being raised from fry and sold together aren't staying together their entire lives and perhaps do fine short term. I don't think it's impossible and probably works out, but it's the longterm that's questionable and risky, as a lot in the hobby have found. Mostly directed at folks who do sororities. A lot of people have stopped recommending them because they have a low success rate in the long run.
That said, I don't breed bettas, but just general pet keeping for me. Bettas have a ton of personality and they vary so much with it, it's a complex thing. Generally, it's likely more successful to keep solo instead of gambling on spending a lot of time and money trying to get groups that end up being totally peaceful longterm.
We recommend mostly keeping certain fish in certain sex ratios, despite stores often cramming all of them together in one tank. It does fine in the store, sure, but it's not a longterm housing. I'd love to see someone keep a group of male only cichlids in a tank and expect it to stay fine in the long run. I think it's something we should always keep in mind with the types of fish that have intense personality variations and have known territorial behaviors that we are gambling and knowing there's many other factors that don't leave it all one size fits all.