Why is Jacob such a bad guardian for the island? by Hurleys Conscience

If Jacob became the “Guardian of the Island” when he drank the wine with his Mother why has he been bringing people to the islands for hundreds of years and doing such a crap job of it?

Is it possible that “Mother” always knew that the Boy in Black (BiB) was always the better choice as a guardian? After all if “Across the sea” showed us that she (appeared to have) killed the other survivors of Claudia's shipwreck then the guardian must harbour a darker side to their character. Maybe she saw the necessary traits required in BiB/MiB and not in Jacob.
Realising that she would never be able to convince BiB to stay on the island and become the guardian she hatched a plan relaying on Jacob's temper to finish the job. Having seeded the idea to Jacob that going down the “into the light” is a bad idea she baited BiB into killing her by wrecking his chances at getting off the island.
Knowing that Jacob would “punish” his brother by the worst way his limited experience would imagine, by throwing him into the light, she waited for MiB to do his bit. (Is it required the the old guardian is killed by the new guardian (providing they don't speak, of course) and maybe why Sayid was sent to kill MiB/Smokey by Dogen). Being thrown down the golden well completes the transition to being the guardian and why she thanked MiB for killing her (without allowing her to utter a word and in front of Jacob) and thereby confirming her choice and completing her plan.

Maybe when Jacob met Richard and recruited him as a moral compass he realised he could bring people to the island. Richard must've told him of the outside world and subsequently we've seen Jacob leave the island. Can the “guardian” leave and return at will to the island?

Maybe Jacob has worked out his actual position in the scheme of things and is bring people to the island to tease and test his brother/guardian.

Maybe the irony is that MiB didn't want the job as guardian and got it yet just yearns to leave the island, Jacob wanted the job but wasn't suitable.

Maybe MiB doesn't realise the reason he can't leave is because he is the real guardian, and has to stay on the island as part of the job. (I'm sure “Mother” wouldn't have explained that in the job description)

Or maybe Jacob got the candidates to the island to replace MiB/Smokey, allowing him to help his twin brother to “rest in peace” and finally leave the island?