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The increase in complexity was followed by the increase in SW dev management tools that help the work across dev teams and the immense increase in computing power to allow validation and testing of various components. Obviously the software complexity is still winning the race, but I can imagine from my own experience with other SW programs that there's a high probability a lot of mismanagement is taking place there.
Despite all this, a great deal of current problems is in third party software and other non-core services. The OS kernel is probably somewhat stable and goes through modifications to cater new cores and platforms.
Regarding Linux, if you need bare minimum you can get by with Slackware or Arch Linux - they would be painful to setup, though.