Personally I've deliberately avoided acquiring a castle or land just
to see how far you could go without that and BtA still probably
managed to end up being one of the most influential (not to mention
notorious) nobles in the game. But I have no illusions about how long
that would last if I didn't bother to keep a large military force of
my own or some of the larger landowners weren't close allies of mine,
so my faction is not really a counter example.
In my opinion, the best, easiest and most realistic (at least partial)
fix for the problem is to drastically reduce visibility of small
groups. For example, two stacks of half a dozen men in a forest
province should only have a few percent chance of showing up in each
others location reports (or triggering hostile settings). The number
of men in the spotting unit should slightly (let's say
logarithmically) increase the chance of spotting. The size of the
to-be-spotted unit should strongly (linearly ?) increase the chance
of spotting. The remaining important factor is the location inside
which the spotted unit is. In provinces chances should be small,
while inside buildings spotting should always be automatic.
Sublocations and cities should fall somewhere in between. One may
even want to adjust the spotting chances based on the province type.
Stacks in forests or mountains should be harder to see than stacks in
plains or at sea. Also some actions which inherently attract
attention (like recruitment) should greatly increase the chance that a
stack is spotted.
On the whole this allows "role players" to go about their business in
the wilderness with relative impunity while allowing wargamers to
contend with each other but without resorting to phony, unrealistic
hacks like "wimpy" statuses.
Other things in Olympia need to be changed to allow greater personal
growth of "heroic" nobles, but this would be a start.