I think the older the "spares" get the more they loose track of how "real people" live. They have a relative careless life (finances are provided, interesting network) and most of them lack a real purpose in life. So they totally overestimate themselves and their importance. Sadly, that is the case here.
I don't think the heirs or the spares have any idea about normal life or what to do with themselves. I also think most of them married people unsuited to be a consort. These women (mostly) see the money and fame.
Charles of UK is the oldest heir - as he did not marry until into his 30's his brother had to "be on hand" in case needed. To give him his due Charles has forged a path in the environmental and disadvantaged spaces long before it was "woke". Had he married earlier and had his own heir then Randy Andy could have been cut loose to do his own thing away from the spotlight. I think Camilla has the right approach as a supporter and not a "Lead".
Moving onto Europe - well -
Sweden - Bitter old Carl G probably has never got over the fact that his son won't follow him ..... but Vic's brother still gets a higher profile than he should - no need for him as there are 2 heirs in front of him. Apparently he would be incapable of any independent achievement. At least Maddie got out of Sweden and has her own life. Daniel appears to have the routine in hand. Not pushy.
Norway - ML is another one who is irrelevant - she and her brother had children around the same time. At that point she should have dropped out of view and lived a private life .... mixed with the same rich strata of society and just showed up at family occasions and a few official ones. MM on the other hand is a but too low key.
Denmark - hmmmm - Jokke married much earlier that Fred so he was "parked" just in case. With no Crown Princess Alex was doing the meet and greet and photo ops. Once Christian was born Jokke and family were surplus to requirements. His second family should never have been wheeled out on the circuit.
Lux - well Henri married young and had children quickly so his siblings were not needed - they seem to have forged their own lives and careers. The family has mega bucks and some of Henri's siblings married into mega money - his sister into Lichtenstein RF and brother who married into the Weiller family. Felix was spare until this year but he also married into a lot of money and got out of the country. MT is "hell on wheels" - no wonder Claire chose to live elsewhere. With baby Charles here now they dodged a bullet.
Netherlands - well they at least seemed to have the sense to prepare the younger brothers to not "be royal" - part of the family but not The Court. The younger sons and families would never need to earn a $ due to the ill gotten gains from previous generations but were well educated and did their own thing - or so it seems. They kept a low profile. As to the current generation - well Max and Wax don't seem to be following in that path - just look at their ill considered actions over many years. Their first two daughters look likely to take "entitlement" to the next level.
Spain - I really don't know - JC and Sofia - just a big NO WAY - Felipe seems well adjusted but his sisters ? Very strange - at least they are either out or way in background now. This is one RF who has to walk a shaky path as they could be dumped again. Will be interesting to see what happens with his younger daughter - I suspect he has learned from the mistakes of his parents and she will be well prepared for her adulthood.
My last observation - these families need to assist their not heirs into a life without the public purse paying for them - education and the rest will happen - there will be plenty of organisations who will put them on the payroll so long as they have the ability - and it they don't then family money can smooth their way into private life.
And as for Titles - nope - if your parent is a HM then the oldest is HRH the rest - no - Prince or Princess but unable to pass that down to the next generation.