Coming from Rails, I spent some time with Django and Flask applications in the last few years. There are noticeable differences between the two of them but both are much lower level than Rails. The developer has more choices and can make more mistakes. Projects can look totally different.
On the other side all Rails projects look pretty much the same and this make onboarding much simpler.
To answer your question: you're probably wasting customer's money (unless you're the customer) by implementing your custom components. You should use as many existing components as you can find: they are probably better engineered (dozens of teams at work vs one person - that included bug reports), better documented and maintained and will live longer. Then you have to adapt much like we adapt buying stock cloths, furniture, etc. But it's cheaper, faster to deliver and usually good enough.
To answer your question: you're probably wasting customer's money (unless you're the customer) by implementing your custom components. You should use as many existing components as you can find: they are probably better engineered (dozens of teams at work vs one person - that included bug reports), better documented and maintained and will live longer. Then you have to adapt much like we adapt buying stock cloths, furniture, etc. But it's cheaper, faster to deliver and usually good enough.