but its size and weight do not allow for firearms that are easily concealed or carry decent quantities of ammunition.
And those are your criteria, so for you, its a lousy choice. For those of us with different criteria and priorities, its a fine round, and not lousy at all.
The OP wasn't asking about what was the best, practical round, or gun for defense, he HAS a .45 Colt Single action was asking what we thought of the round for defense.
being "easily concealable" and "carrying a decent quantity of ammunition" were not asked about.
To me, whether or not a round is good at its job is about what the round does when it hits its target. Not about the advantages or drawbacks of the gun its fired from. Those pros&cons are valid questions, but they are a different question.
The .45 Colt (or that rose by any other name) has been stopping two and 4 legged beasts since 1873 reliably enough that it is still made and used today.
Might not be your optimal choice, but that changes nothing about what the cartridge does, can do, and has been doing for 149 years and still going...