Policy Statement on Address Space Allocations

True. What this protects against is losing the tail circuit to either
provider. If the primary provider is single homed to the rest of the
world or is otherwise unreliable and their entire aggregate disappears
from global routing, then you lose connectivity to providers blocking
long prefixes. I think that is the best you can do as long as some
providers plan to block your long prefix.

Pick a very stable aggregate to cover your long prefix.