Yes, a one-gallon tank is certainly better for a betta than the small cups where they live in the fish store. A one-gallon tank is also better for a betta than a mud puddle, a glass of lemonade or a washing machine. Just because it is better doesn’t mean it is ideal or correct.
The reason bettas are marketed as a disposable pet is that they can survive horrible conditions. This leads people to think that just because their fish survived for years in a bad situation, it really doesn’t matter if they follow proper care guidelines.
To me, it does matter. I see no point in keeping fish if I can’t give them the best home possible. Keeping a betta in a plant vase, tiny bowl or small tank misses the entire point of having the fish. If I can’t be a responsible steward for a living thing brought into my home I’d be better off with a pet rock.
It’s also erroneous thinking to try and “save” bettas from the cups in the store. Think of this from a marketing perspective. These stores don’t know you are trying to rescue the fish. The only know that you bought a fish, and that will lead them to think they must be doing something right. So, they stock more fish.
It’s better to buy bettas from places you know follow smart stocking practices. They keep small numbers of fish on the shelf, not piles and piles of containers as you see in some of the larger chain stores, and they sell them frequently. If you don’t know, ask someone at the store. You may have to look around town to find the right place where you feel comfortable buying fish.
Better still, if you don’t like how bettas are treated in stores, don’t buy them at all. If people don’t buy them, the stores won’t stock them.
In the end, it is up to the fishkeeper how they wish to treat the fish the in their care. Bettas are marketed as disposable pets that can live in tiny tanks or other bad situations. If you keep them that way, you are playing into that marketing.