Soup making - should I add extra water and boil off for flavour? When making soup, my husband likes to add a lot of water then boil off for 30-45 mins to make it more concentrated.

I prefer to add just enough water for consistentcy then gently simmer, thinking that adding the water will just dilute it anyway, defeating the purpose of then boiling it off. Plus then the contents get mushier..

Which approach is recommended - or will both end up with a similar result?
My experience and the recipes I read are to simmer.  Hard boil and simmer are the same temperature so cooking time should be the same.  A hard boil can break up contents.  Hard boil also dirties your stove top.  That said even with a simmer you can sometimes need to add liquid.

If your husband wants to hard boil there is not much harm.  He is cooking.