Drawbacks to a very large dog...
Space, in your car, for a huge crate, lying in the middle of your doorway...or even better behind the door when you're trying to open it, lol.
They cost more to run, food costs a lot as does insurance and vet's bills. (Much bigger amounts of everything) You can't buy any old toy as they just don't stand up to big dog play.
If you get a puppy, there's a couple of weeks where you have to carry them around...but they're really heavy, also they get to adult other breed dog size and still behave like puppies (because they are) and other dogs and people tbh are fairly intolerant because they're already huge.
You're going to at some point have nearly 8 stone of dog to move, either because they're too young to be jumping in and out of cars, after operations...even just neutering or if they get ill or old and infirm.
If they ever do have a bit of a behavioural issue - a big dog who barks at dogs is reacted to very differently than a small dog doing the same thing...if they ever develop a major issue you need to know that you can hold the big dog do that it's under control.
They tend to do things like knock over small children by accident just by brushing past them.
They usually don't know they're big and still try to do things like sit on your knee, lol.
They tend to be slow developers and so you get naughty puppy behaviour for a few years, then they don't live as long, so you only get a few years of adult dog before they're old.
None of those are reasons not to get one, but, they might be things worth considering.