Personally i'm already concerned about segwit.
You know, a team of 5 or 10 people creates something, puts it in the wild and then millions of hackers try to attack it. See the odds?
once upon a time bitcoin was the job of one guy. even when it started to go places it was looked after by a small number of people. that is a very good point you have but i'm pretty sure these people know what they're doing. it's not like building something from scratch.
everything that's come after kinda tells us everything we need to know about trying to introduce complexity. someone out there is cleverer and nastier than the creator.
btc wasn't flawless when it was created. Many bugs were discovered especially early on. No matter how good your expert is, there is always something they overlook. One person has only one perspective on things and will without a doubt fail to see all the possibilities.
New technology means new bugs. Sure they don't build from scratch but the new things that are introduced are new potential troublemakers. It's just the nature of the thing.
These networks are accessible by anyone with an internet connection. It's really the dev team plays against the rest of the world.
The mindset that's needed by a sucessful coindev is a love of minimalism and good security awareness.
Devs who want to inovate a lot of things and create coins with lots of new features will fail in most cases.