It's adorable that you created a neat little table<Sally Field Oscar speech> I'm glad you liked it!
where the enemies are standing adjacent to each other to illustrate your point that Cleave is useful, when my entire argument is that you can't expect there to always be enemies standing next to each other.If none are adjacent, then Cleave is out, but Cleaving Finish is still on the table. -- Even if the character never cleaved, the feat is nonetheless worth it as a tax toward Cleaving Finish.
All you're proving is the usefulness of a reach weapon on a large creature. To which I would say, no duh.
How dare we discuss optimization in an Advice thread!
The build Slim Jim is suggesting is a valid build, but does not help the original poster (who) clearly stated that his character is a 3rd level barbarian that is looking at cleave as his 5th level feat. If he followed Slim Jim’s advice he will be able to get everything by 17th level assuming he has a 13 INT. 17th level is not my definition of early-mid level.
You can take my submitted build up to just 3rd, and then branch off (i.e., not going all-in with Repositioning, etc.; Great Cleave is also probably superfluous, as while two enemies adjacent is pretty common by happenstance, getting more than that bunched is difficult without planning it).
If his game has the Retraining rules, at 5th the player could have the build as I submitted at 3rd, plus two more levels of other classes of his choice, and be contributing a lot more than your standard greatsword charge-monkey.
All you have to do to wreck multiple-opponent encounters is exist and swing away for a few rounds. From what I've seen in most APs, whenever groups of enemies are thrown out, the individual enemies are too weak to do anything.
From what I've seen in APs (with the exception of some particularly punishing fights) all you have to do to wreck encounters is exist and swing away for a few rounds. ¯\_(ツ)_/¯
In APs, the most memorable fights tend to be those against incorporeal undead at level one, or when your boat's boarded by an invisible wizard three levels your superior. But not all multi-opponent fights are forgettable, and, in fact, they're easy to make memorable indeed.
There are two different methods of making good group fights. The first method is to have just enough opponents to negate the PCs overwhelming action economy, but not enough that any are irrelevant. For instance, a party of four antagonists, each of the PCs' level (though one CR lower), would make for an awesome boss fight against four PCs. The second method is to have one lead adversary of about the PC's CR, and then an overwhelming number of minions. Ten or twenty or however many. Each of them might be individually irrelevant, but if the frontliners choose to ignore them they'll go after people with less stellar defenses.
While the PCs collectively easily win encounters all AP long, individual PCs will croak here and there. Having a Cleave-guy in the party mitigates a common cause of character death: being mobbed by multiple assailants crowding in to dump all their action-economy on single targets. (How unfair that they pursue the same tactics the players do; who told them they could do that?)
It's especially nice when the death you prevent is your own.