It isn’t always easy to stop the hogs eating bird food, but there are steps which could be taken to minimise how much they can get, by making a few minor changes. For instance, perhaps you are putting too much food out for the birds, if there is that much left? All the species you mentioned, as well as dunnocks will happily eat off bird tables or bowls/plates/dishes/trays on the ground. They may spill a little but they usually eat most of what is spilt as well.
However, you did say “I put out three dishes with a mixture of suet pellets, mealworms and Go-Cat kibbles, hard ones and soft-centred pockets, the last two seem to be particular favourites, the eat the lot!” So, I would suggest that you cut out the suet pellets and the mealworms and just offer them the Go-cat kibbles and soft centred pockets – i.e. cat food, which you said they liked. The cat food doesn’t have to be wet cat food.
The one who died clearly did have issues, but another time you might be able to save a hedgehog by getting help for it from a hedgehog carer, as suggested above.
I have heard mention that hedgehogs are likely to become extinct by 2025 – just a few short years. It is up to those of us who love hedgehogs to do the very best we can for them. Every little thing we do might make a difference.
This week is Hedgehog Awareness Week