In college, I made a website and I thought another student "stole" the idea. I considered my legal options, but I'm glad I stopped there, even if I did have a case.
The other student was never a serious threat to my idea and in fact lost interest in the idea next year. So the only harm I suffered was to my ego that thought I deserved power over others just because I had an idea slightly before someone else.
I buy into Radon's argument that Replit has substantial value outside of "eval()" and is not actually threatened financially. As a result, I could understand a founder feeling disappointed at discovering clones, but I think it's important to separate harm to ego from harm to livelihood.