No, if feedbacks worked as you describe, negative feedbacks would be just as destabilizing as positive ones.
It's two sides of a coin; given an initial forcing in one direction (e.g. warming) a feedback may be positive and amplify the response (e.g. warmer air holds more water vapor which enhances greenhouse effect and further warms the air). If an opposite forcing happens (so, cooling in this example) the same feedback mechanism amplifies that response (cooler air, less water vapor, further cooling). Run away in either direction and you've got an uninhabitable rock.
A climate feedback mechanism is therefore only positive or negative by virtue of the context. It has no intrinsic directionality. Therefore talking about a long-term dominance of negative feedbacks is meaningless (or worse).
Either I don't follow or I don't agree. Surely the feedback is either in same direction as the forcing or in opposite direction to the forcing therefore does have directionality.
So 6 possible situations:
1. Positive feedback, gain of less than 1. The result is larger than the forcing in direction of forcing but situation doesn't run away.
2. Positive feedback, gain of 1. Steady movement in direction of forcing. Can only have an unstable equilibrium.
3. Positive feedback, gain more than 1. Run away situation in direction of forcing. Can only have an unstable equilibrium.
4. Negative feedback, gain of less than 1. Moves in direction of forcing but result is a smaller move than the forcing. So it is hard to get large movements.
5. Negative feedback, gain of 1. Situation oscillates in direction.
6. Negative feedback, gain of more than 1. Oscillations become larger and larger so a run away situation of unclear direction.
When there are two or more feedbacks the situation becomes more complex.
In climate there is usually a weak negative feedback from warmer earth emits more radiation and we are thinking about feedbacks that hopefully have gain of less than one within that environment. Positive feedback with a gains of more than 1 can exist in some situations but such mechanism will usually run out of some necessary ingredient for the feedback before you get a Venus or complete iceball situation.