The thing is, many names are cyclical. Even classic names. Isobel is a prime example of a cyclical name - an old, very established name that goes in and out of fashion.
Even Royal names are more or less popular, depending on the era. No-one was called George when I was born in the 70s, whereas it’s more popular now. Likewise, Victoria was reasonably popular in the 1970s, but not many babies are being called that now.
Of course - there are always exceptions - it’s not an exact science! But we all know Victoria, for example, is not a popular girls’ name right now.
Other ‘classic’ names which are not particularly popular right now include Michael, Simon, Robert, Richard, Peter, Jane, Anne, Sarah, Mary (Mary is very possibly on the cusp of a return).
The whole point is that names - even classic names - go in and out of fashion. As soon as they become over-used and begin to sound tired, people stop using them, for something that sounds ‘refresher’ to their ears. Which is often why grandparents recoil in horror, as what sounds ‘fresh’ to modern ears, inevitably sounds old-fashioned to older people, who have memories of their peers being called those tired (to them) names.
This is also why some people really don’t want a popular name for their child. It’s the popular names that sound extra dated in 10 or 20 years, and become heavily associated with a particular generation.
I think if you want to be ahead of the curve, you give your DC a name from your own parent’s generation. It will inevitably sound dated right now.
But by the time your child reaches adulthood, that name will probably be part of the cohort coming back into fashion for babies being born then.
It’s a risky little game though, as you don’t know which names are going to be re-viewed favourably, and which ones never really fall back into favour.
The other option is just to go with the lesser-used names that don’t have an association with a particular generation. But it can be hard to land on one you love. Shakespeare is often good for this sort of thing - Miranda, Helena, Juliet, etc. Also names like Ursula, Cecily, Phoebe, Felicity, Briony…