very self sabotaging to withhold information just for someones ego whose personality is so irresponsible that he could cause problems worse than the existential crisis at hand.
and what is with the obsession over the designation "baggage carrier"? that is just the job description. he could take on another designation with more valor to it, then there would be no chance to insult the hero's ego in the first place, right?
The problem is, the hero is petty as shit. If would not be able to accept any help at all. Anything that diminishes his feats. If he orders them to do it then he is in control, its his order. But he will probably demand they don't assist him in key fights. That the buff is just automatic, and that its so powerful. He wont know if its the buff or his own power, and worse, others will question if it was him or the buff.
A flashy title wouldn't change this. He had to get lied to. The problem is the MC is not able to visibly contribute, they couldn't call him a mage, or a support, they needed a roll that lets him just stand nearby and seemingly not be part of the fight. So baggage carrier fits well. But the title is only a insult when the hero uses it, the king and others know what it really means, and know his real power. Hell the guild seems to even know as a whole, his rank was S, so anytime they ID him they know that the role is BS. It is a extremely surface level disguise, he got proper credit.