Should it surprise anyone that criticisms of a gov't are more likely to come from people opposed to that gov't than those who support it?
It's a strong indication that such opposition is politically motivated. It shouldn't matter if you're left or right. And no, it doesn't imply it's fake news. I haven't used that term. But when there's so much bullshit out there, it's important to not put too much stock in what you think is an indisputable fact.

That's why I say I don't care if the UK gov't had the best intentions, I care about what they actually did and whether it was a huge collosal fuckup that is costing us thousands of lives. Which it was, and it is.
I do care about intention. I also care about competency, but this suggestion of your that such incompetency has cost thousands of lives, that is not a fact. This is the kind of accusation that needs to be hashed out in court, at the right time.

I'm also not concerned with parsing the responsiblity between the gov't and its team of advisors, because ultimately the gov't decides which advice to listen to, and so they bear the ultimate responsibility.
You use an important word here... ultimately. I agree, but for me "ultimately" means when all the facts have been established. They haven't yet.

If they got bad advice and followed it, then they should have hired more competent advisors.
This is an untenable position. How are they supposed to know their advisers are incompetent until after they have demonstrated such? The question then is should the government have known? We can't know this, but it's so easy to say it.

If they got good advice and ignored it, that's their fault too
Indeed, and if this is established at an inquiry, I'll agree they should be accountable for it.

There's no excuses about quality of advice that absolve the gov't from blame if things go wrong; that's not how responsibility works.
My argument remains the same. Inquiries are the correct forum for accountability.