The powers of full Betazoids aren't really specified either. Are they able to share as much as Vulcans do when they do a mind meld or are Betazoids just "talking" but silently and over a long distance?
Vulcans' mind meld is much more potent/intimate imho, not just two minds communicating, sharing of consciousnesses, gleaning of thoughts/minds, or having sense of one another's being etc... but more of a merging of self. Per the reports, when they come away, part of the other is now a permanent part of them.
I expect it's entirely possible for them to completely pass their entire consciousness into another body/mind, & in a sense, become as immortal as a Trill, but without any physical hosting. I'd imagine their respect for whatever other being they'd be inhabiting is the only reason they don't do it, except for whatever end of body life ritual they have, like willful joining or enshrining in a vessel of some design.
This kind of transference would seem to be the ultimate mastery of telepathy, & would suggest they have the most powerful ability of any telepath... which would also mean they likely have all the other levels of telepathy too, but for whatever reason have either willfully rejected those traits, neglected to bother with them, or are actively choosing not to practice them.
Full Betazoids however, really only seem to know what people they are engaging with are thinking & feeling in that moment, which isn't even as strong as Ullians, who can delve into people's memories, or a Lumerian, who can somehow feed on people telepathically