I would not keep an angel & any labyrinth fish together in such a small tank. Paradise fish have cooler water needs than angels & have a "pugnacious" reputation, I have not kept them in part because of that.
In a 20g you could have 1 of either dwarf, pearl or honey gourami Or a betta OR an angel. Neons are the natural food of angels, not a great choice. All schooling/shoaling fish should be kept in groups of at least 5 or 6 as a minimum. More are always better.
Be very careful with online research, you can almost always find someone to support whatever view you desire. I would be ask how long & in what size tank they had success with any combination...& what size were their fish? Many fish like angels are sold as juveniles & it may be up to ~ 2 years before they reach adult size. Most of the commonly available species should live 5-10 years with good water quality, food & care, barring a disease disaster (not related to care or poor stocking). Bettas tend to only live 3-5 years due to the extreme line breeding to create the lovely fins & colors.