On our 'worst days' it's 3 hours, I'm home for an hour at lunch, then another 3 hours. I have two dogs. This is prob around twice a week.
The other 2 days they are left about 4 hours in one block
The other 3 days they have someone full time.
The rest of the time are filled with dog days out, dog activities like full training days, days doing scent work, agility, long walks.
They are left in a comfortable, warm room, with background noise and some form of enrichment activity like a kong or nylabone. They are walked before and after being left.
I'm sorry, but these dogs have a great life. Thousands of dogs spend their lives in kennels, locked in the kitchen, get a walk round the block once a day. My dogs sleep all day as they've had walks filled with training, enrichment games and swimming.
I think you have to think carefully about what breed etc will suit your environment but both me and my partner work full time and make it work through working different hours and me going home at lunch time.
All of that said, leaving a dog 8 hours a day every day is cruelty, if for no other reason than that they will need to go to the toilet.