I have a feeling the hero party was not being dicks just because that's how they are.
It may be that the hero party figured that the MC is not strong enough to continue the fight against the demon lord and his forces.
Realizing they are not strong or capable enough to protect the MC in the upcoming fights and out of concern the hero party used the "we don't need you" trope or the "beat the dog to fear and run away from you even though you care and it kills you on the inside" kinda trope. Otherwise I bet the MC would not leave and end up getting killed.
But that's just me being hopeful and knowing how important some one like the MC can really be. Even if he could not fight.
The skills, ability, and benefits he brings along to a party most likely out out shine any failures he may have.
I'm guessing the MC did most of the cooking, cleaning, maintenance, lookout, baggage handling, and even some crafting along with his animal taming ability.
And to top it off, the MC seems like a nice person that most people would like.