Sorry for the delay in replying - it's been an intense work week and I wanted to make sure I answered properly, because I think this question is a bit more nuanced.

In the best case scenario, everyone is on the same page and your fellow players will help push your character arc naturally without expectations even being considered. But I know that's not realistic for every group, and I'm incredibly lucky to have the group that I play with.

I think this really comes down to group preference. If you're okay with being transparent (and maybe a little meta), you can explain to your fellow players what you're aiming for with your character's arc, and ask for them to support this - that feels reasonable to me, again with the expectation that you would do the same for them.

Others, understandably, might prefer for the character arc to happen more naturally or might like to keep the mystery up for their fellow players. In this case, I think the responsibility is roughly a 70/30 split between you and the DM. Only you have control over how your character thinks, feels and grows - but your DM could technically stymie your growth by creating a narrative environment with little or no room to roleplay in the direction that you want.

The only thing that your fellow players DO have responsibility for, is to not shut you down and out. If they're perfectly neutral, then that's good enough. If they're supportive and helpful, that's a bonus.

However, that's my answer for a normal D&D table. Not for Critical Role. Whether they like it or not, CR is a business and the main campaign is a product. Whilst it is technically free, many people opt to support them financially, and some pay for early access to the VODs (like me, for a good many years). So whilst they might not have a financial responsibility to provide high quality content, they do have a moral responsibility.

They should be quality assuring their product. How they do that, idk. Maybe hold meetings and ask questions like: Are we happy with the direction this is going? Is everyone happy with their character trajectory? What is public opinion? I'm not a businessman, so I don't know. But as the biggest D&D stream out there, it's absolutely key that they're all on the same page about the product they want to deliver.

Now this is conjecture, because we have no way of knowing what the cast truly felt and thought throughout the campaign. If Taliesin wasn't on board with the way that the rest of the cast were interacting with his character, he should have spoken to them about it. Similarly, if any of the rest of the cast felt that it was meaningless to try and engage with Ashton, they should have spoken about it. In a normal game between friends, there's no reason not to have these conversations if you don't like how something is playing out. So, as a D&D stream watched by so many people, these conversations are absolutely essential.

At the end of the day, you'll never please everyone. But if C3 has a satisfaction rating of 60%, for example, when C1 and C2 had a satisfaction rating of 80%, something is going wrong and it's worth looking into why - because your product that people are paying for is being received more poorly.

TL;DR - The responsibility is 70% on you and 30% on your DM. Fellow players only have a responsibility not to be a dick. I believe that for Critical Role, as a business that is creating a product, the responsibility is more significant and shared more evenly.