The universe simply doesn't contain enough material to halt its expansion. I can't see any reason for bringing in an additional parameter. If the universe is lighter than scientists thought, and has been expanding more or less steadily, than it would be older than one filled with more matter. Such a young universe causes a serious problem. The oldest stars in sight are thought to be 14 billion to 15 billion years old.
Gravitational attraction moves huge clusters of galaxies around in ways that can be measured.
But when these measurements are made, something is missing. The movement obviously takes place, so there must be more to celestial matter than meets the eye. The universe must contain a great deal of invisible, or dark, matter. But with a lite universe that's going to expand forever, less matter becomes missing. But now it's much less, only about 15 percent of the mass of the universe needs to be dark.