It's not that fine a line. There's tons of space in the middle and I find a steady supply of coworkers who love to write code and hate to use libraries who never bother to understand half of what the libraries they do use are capable of. I may be slightly unusual in my habit of trying to find new uses for the tools we already have, but I'm not abnormal. This is something mature people should be doing as a matter of course.
This "everything sucks (from my myopic viewpont)" thing is like a bizarre form of learned helplessness. And I say that as someone who complains a lot about the quality of tools and libraries. Only about 10% of the time do I think that means we should write our own. 40% we should pick a different tool, and half the time we should try to convince the author to fix the worst aspects (when the problem is deeper than a PR can address).
Code you wrote is easier to understand for you. Of course you're going to be more productive with your code but what about everybody else? Are you making any compromises for the comprehension of others? Do you remember nothing about middle- and high-school coaches complaining about 'ball hogs'?
The optimists think all of their code is amazing and bug free and hence cheap. But it costs everyone else time, respect (either for you, or themselves), but perhaps most importantly, resume material and independent support options. You are hijacking the project to fluff your own ego.
For me, the worst quartile of my jobs have been NIH that turned into codependent bullshit drama, and it causes a pretty intense histamine reaction (as is evidenced in my phrasing in this comment) for me with people who are not self-aware enough to allow at least the possibility that maybe 50 people who have been thinking hard about a problem for five years are better equipped to solve it than you can in a week of bravado, followed by months or years of dodging responsibility for the problems you created by substituting your judgement for the rest of the team and the entire Internet. Just get over yourself and be a team player for once in your miserable narcissistic life.