Why the focus on second homes? I would care more about utilisation of homes by home-owners: walk around London at night, so many apartments are dark. The locals say investors own them.
More housing. A holiday home should be an utterly normal thing for a middle class family like in Finland or Spain.
As long as residential homes are a vehicle for investors rather than _living in_ (by the owner) you will have a problem.
Make building housing legal again.
Also. Renters deserve housing too. Restricting housing to the owner occupied is a great way to hate things by social class but I see no reason to further favour a population that’s richer and more powerful than the rest of the population already.
https://www.service-public.fr/particuliers/vosdroits/F59/per...
The resident might be at work, at the gym, out for dinner or at the cinema, at a friend's house, in another room, might have good blackout curtains and only use lamps for ambience instead of the ceiling light, on holiday. I bet if you stood outside one of these buildings where "most of the lights are off" for the entire evening, you'd see lights come on and off, and in aggregate find that most of the flats were in fact occupied.
By the same logic, I could look outside my window right now, count zero cars driving down the road and declare it a useless waste that nobody uses.