The prevailing view (from the medical model) is that Bipolar is 80% genetic and rare with a 1% prevalence rate. And some feel it is as severe as schizophrenia and can only be treated by medications.

Depression on the other hand is common and has degrees of severity and recurrence. It does respond to treatments of various kinds.

Both lead to intense suffering and possible early death. Both can ruin quality of life. And within Bipolar, the manic or hypomanic phases are treated more seriously than the depressive phases.