I think you are confusing showmanship with the ability to run a country in the state they come to the position and how much they can do from that point on.

Yes, showmanship is ever more relevant in winning elections, if not has been the most relevant thing even before. So it makes sense to put forward a good entertainer to win an election.

What you are wrong about is that most of the time, show people are just goddamn big liars and completely incompetent fools at ruling anything. It is fitting, tho, since all they do in their primary skill is to make people forget about problems by making them pay for a brief period of entertainment, nothing more.

Biden is an old bastard with a foot in the grave. He shouldn't be out there running a country, but the current alternative is Trump that just plays to the audience and has no experience or aptitude for directing.

Yes, Biden should not have been running for president, and a balanced mix of showman and leader should have been out there instead, but who is that or who was that? A no-name in the political sense can't be considered a showman, and we saw what other options could the left procure without stooping to Trump levels. They were not enough of a showman at all. So, why not go with the decently-competent decision maker instead of an unfunny showman?

The blame for not producing a balanced showman and a decision maker falls on two groups: One is the political organization of the Democrats, the other is their voter base. The political organization is corrupt to an extent no matter what you do about it. People with power careers form pacts within pacts. A full education reform is needed for quite some generations to get rid of tribalism and corruption. The voter base is irresponsible. They have lots of other responsibilities and pursuits in life, but a core decision about these falls on taking on the political responsibility, maybe more than other decisions directly affecting the daily lives at this period of the world's history. Voters should not isolate themselves from being a talking part of candidate production of the political organisation, even if they don't actively take part in the local representation. Even just been keen about which names are being talked about in the political organization would give the voters years ahead of an election, and those years would decide if a candidate candidate is popular or not liked within the political organization. Voter dislike for a candidate months before the election, and when the campaign process has already started, will hardly make an impact on even bringing the topic to a discussion of a change of candidate, let aside producing a better one.

On the contrary to asking for a change in candidate for a better one just months before an election is a complete show disunity, and such a lack of show of unity in voter base is even more damaging than a lack of show of showmanship in a candidate.