You are not being unreasonable, the truth is there used to be a point to monarchy in its hayday.
Monarchs used to actually lead and even though succession was hereditary, monarchs still needed the support, including the financial support, of the court and ultimately the country to rule. It wasn’t a fair and democratic system, but you could maybe see the arguments for it in terms of stability, consistency and having a single vision for an otherwise factional nation. Then you have the fact that these people used to be educated from a young age to rule, they spoke lots of different languages, they trained in military strategy, theology and philosophy, they married monarchs from politically useful countries to create alliances helping the country to stay safe and prosper. The magic blood aspect of their reign, ridiculous though it is, was only part of the story back then and you had all sorts of battles over who was the rightful heir, so ironically, it did used to be somewhat meritocratic back in the bad old days- If you were bad at leading the court, if you were a terrible military strategist (see tzar Nicolas II) or if you were just generally seen as “showing the country up” there were ways of replacing you.
What do you have now? A monarchy with little or no role in terms of political, spiritual or moral leadership apart from a vague sense of upholding tradition. They don’t appear to do much good for their people, if they do it seems to be very difficult to quantify. They give each other medals and titles on their birthdays just.. because. The don’t pay taxes on much of their fortunes, and despite being a public institution, they are exempt from public scrutiny through official channels that the parliament and civil service are subject to.There is no one who will challenge them, not even another royal faction, for their position so that family just gets to accumulate wealth from the country generation after generation without having to ever earn it or reinvest in the country they are the figure head for. Given their access to resource few of them seem particularly gifted or impressive, so they don’t even particularly make the country look good. To be fair, the queen is a very good diplomat, but she didn’t do a great job raising good diplomats for some reason, so she hasn’t even produced decent heirs to replace her, surely that has to be part of the already very limited JD?
They seem like an expensive ornament which bakes deep class inequality into British society. After all, if the royal family is definitionally more important than everyone else, and there is no pretence that they have to do anything to earn that importance, or could do anything to lose it, how can we aspire to have a fair society? Very few people even believe in god anymore which is supposed to be the other source of their power and virtue. Proof of the unfairness of the society is therefore seen in every stamp, every 10 pound note, every royal crest on a fine building you’re not allowed into (though your ancestors likely paid for it with their money if they were nobility or their blood if they were peasantry).
Having said all that maybe they should be kept because tourists like to come look at the novelty of it all and that probably brings in more money for the country, possibly. Also pageantry.