It’s worth starting a startup based on an idea even if it is easy to copy.
First of all, it will take competitors a long time to realize that your idea is even a good thing to do.
Even when competitors realize your idea is good, (a) it will take them a long time to implement and (b) they’ll probably screw up critical things.
And finally, working on your ideas will lead you on to new ideas. So you’ll be a moving target; by the time competitors copy what you’re doing now, you’ll be doing more.