I say this as someone who has two rescue dogs, has worked in puppy classes/assisted with behavioral classes and with rescues. For first time dog owners - don't get a rescue.
They are not only bred for looks, many breeds are predominantly 'working lines' or might have working and 'show lines' Kelpie's are pretty much breed for work, one sold for $49,000 last year as a results of it's impeccable breeding, because it was capable of doing the work of 8 humans. They are an exceptionally healthy breed. GSD's are an example of the stark difference between show and working line.
How long a dog lives is size dependent, The bigger they are the shorter the lifespan. Given that many rescues are some kind of staffy mix - a small to medium size dog, of course they are going to seem to live longer.
Facts - While pure bred dogs are more likely for about 10 genetic disorders (dependent on breed) many of which can/are tested for and can be prevented by owner (bloat) - overall mixed breeds are not significantly healthier. The point at the end about pure breed dog owners being more likely to get veterinary care rings true in my experience. Many rescues have extremely poor physical structure (poor breeding/incompatible mix) which meals the activities and exercise you do should be carefully selected.
I know the breeders here will refund or take the dog back if it ends up with a significant health issue . If you cannot care for the dog anymore for whatever reason the dog goes back to the breeder - it's not contributing to the excess of dogs - that is the fault puppy farms, backyard breeders and those who chose dogs based on looks.
Mixed breed dog coats can end up being very expensive to groom and properly maintain, because you get a wild mix of coat types that need different styles of grooming. Professional groomers that treat dogs well often won't work with mixed coats.
Last year I could have purchased about 8-10 pure breed dogs for what I paid in veterinary bills in one month on my 'cheap healthy rescue'
From working puppy school, it is the pure breed puppies that had the best temperaments, and research also supports this. Many of the mixed breeds showed early signs on potential anxiety issues.
So for new owners having a dog with a breeder who will be a fantastic support and fall back vs the lucky dip of rescues. Learn how to be a great owner with a dog with a rock solid temperament - don't do the lucky dip - project dogs are incredibly rewarding - but they are better placed with those who can give them everything they need, not an owner thrown in the deep end.