Who makes the bottom of the pecking order when it comes to durability?
Canon and Nikon probably do. I can't imagine anyone making a DSLR or mirrorless more "disposable" than the newly introduced Canon 4000D (not even offered in the U.S.). It also has the lowest MSRP of just about any interchangeable lens camera on the planet with an APS-C size sensor. But you won't spend a few thousand bucks on one of these cameras, you'll spend a few hundred, even with a couple or three starter lenses. You get what you pay for.
Who makes the top of the pecking order when it comes to durability?
Canon and Nikon do. The Canon 1D series and the Nikon D3/4/5 series are legendary for the amount of use and abuse they can take and keep doing the job. You will spend several thousand dollars on just the body. You have to pay for what you get.
How can this be?
Simple: Canon and Nikon offer a far broader range of camera bodies than other camera companies do.
They also offer a far broader range of lenses than other camera companies do. Not only with regards to durability, but also with regards to capabilities, features, and performance.
If you want a lower end camera that is tougher than the average entry level body, look to Pentax. They tend to make their entry level bodies aiming at similar durability standards that Canon/Nikon put in their enthusiast bodies.
If you want a higher end camera body that is all about making a spec sheet (including very good sensor performance) look good but can't stand up to the most punishing conditions, buy a Sony. Just don't use it around water, sand, or, heaven forbid, salt water.
Olympus, Panasonic, and Fuji are mostly bunched up in the middle. They don't make any bargain basement entry level models, but they also don't make any top end professional "flagship" models built like tanks to take the kind of abuse photojournalists, war correspondents, wildlife and nature photographers traveling to exotic and remote destinations all over the globe, etc., put their gear through, either.
Leica is a very low volume brand that prides itself in being a status symbol. At one time their bodies were all hand built and individually assembled. They may still be made that way. But in terms of performance and reliability, they're nothing extraordinary. They're just marketed at folks who will buy something, anything, because it is too expensive for most other folks to afford.
I'm sure there are some folks that will staunchly defend "their" brand as the best ever and argue the merits of their camera based on "data" they've found from any source imaginable containing every metric ever devised. There are those who will call the above statements biased and nothing but blatant "fanboyism."
But the above generalities are gleaned from years of personal experience, the personal experience of other photographers with whom I'm acquainted, and by reading a lot of reports from folks such as Roger Cicala, the founder of lensrentals.com. Roger's company not only rents lenses, they rent cameras too. Lots of cameras. Cameras from most of the major brands along with a few "minor" brands. Roger likes to blog about what he finds taking cameras and lenses apart when he "needs" to repair one of them.¹
Having said all of the above, it there's one thing anyone who has read Roger's blog for very long should have picked up by now it is this:
Every camera model from every manufacturer can break. All of them. Some may break more often than others.² Some may break under conditions that others would most likely survive. But no camera from any manufacturer is indestructible. None.Of.Them. Not.A.Single.One.
As we've already stated, with most cameras you get what you pay for, and you have to pay for what you get. Sometimes what you are paying for is more features or higher image quality. Sometimes what you are paying for is better handling with more controls and faster autofocus and frame rates. Sometimes it is good build quality and a reputation for durability. Sometimes it is for a network of service centers that have a reputation for taking care of their customers. Occasionally it is for the cachet of being the only person around with a specific logo on the front. For most cameras, it is a unique combination of all of these.
When you buy a camera it is just like buying a car or a boat. You make your choice, you pay your money, and you take your chance.
¹ Sometimes Roger and his sidekick, Aaron, will take the earliest opportunity possible to disassemble the newest, hottest, camera model on the market. It's something they would need to do eventually anyway, since they write the repair manuals for the technicians at their company who do the routine day in and day out repairs that can't be sent off to a service center (or come back from a service center still not right).
² Roger used to publish a semi-annual list of various cameras and lenses and their failure rates at his company. The advantage of someone like Roger publishing such a list is that the sample size of cameras owned by any company that are actually used on a regular basis, rather than stockpiled in warehouses waiting to be sold, is probably larger at his company than just about any other single entity anywhere.