Are you criticizing the experts here? Careful that's verboten.

I'm not, no. As more evidence is accumulated to support a hypothesis, it is rational to strengthen one's belief in it. All beliefs should start out weakly held, until sufficient evidence is gathered to either reinforce or change them. And of course even strongly held beliefs should be re-examined if sufficient evidence piles up to the contrary.

So the incorrect opinions based on weak evidence that the experts had over the past years of covid should not have been "reinforced to others"? That sounds to me like a criticism of the experts.

No, the experts were disseminating the best available evidence at that time. I will criticize some steps by policy makers, like stating initially that masks were ineffective when in reality they were trying to discourage mask shortages to keep them for essential workers. I think in cases like that it's better to be honest with the public. But I don't have any criticism for scientists who accurately portray the best available evidence at a given time.

My criticism was for the the hypothetical that the OP may have rationally stated that the virus was nothing more serious than a seasonal flu, based on experts stating that borders should not be closed. The statement that borders should not be closed was based on the most relevant research at the time; it turned out to be incorrect and was later reversed. But as a lay person, making the jump from that statement to the opinion that the virus is no big deal, and then echoing that opinion to others as fact, is not rational. One might have taken it as weak evidence in that direction, but no more than that.

If "experts" were saying not to wear masks, insisting that border restrictions were racist and xenophobic, telling people to go out and gather in large groups in public, then OP said absolutely nothing wrong by claiming it was no more serious than the seasonal flu.

Now we know that some "experts" were just totally wrong and had no idea what they were talking about, and others were in fact spreading misinformation abouta pandemic for political gain. But that is not OP's fault. You can't condemn him and absolve the actual people who reinforced that incorrect information to him in the first place. Ludicrous.

From the very early days of the Wuhan outbreak it was clear, and was the consensus of experts, that the virus was much more serious than a seasonal flu. There was indeed disagreement as to the best ways to combat it, but it was not said (by anyone credible that I saw) nor implied that the virus itself wasn't serious. I'm sure you could find an occasional counter-example, as there are going to be people in any field who are wrong about any given subject, but the consensus was pretty clear. (Note that I'm talking about actual experts, not politicians or pundits.)

What data do you base your claims on?

Studies like this one, https://journals.plos.org/plosone/article?id=10.1371/journal..., do not support what you are saying. Experts predicted 30,000 people would die from covid in the UK by the end of 2020, compared with yearly deaths from influenza which is usually quoted at about 25,000-30,000.