Is it? The costs which you offset with developer productivity get multiplied times the number of users, which is orders of magnitude more than number of developers.
And value delivered also gets multiplied by the number of users. VS Code users decided that they like it even after accounting for Electron. Clearly, then, VS Code has certain strengths, and I'd argue that some of those strengths are made possible by Electron. Second, great design requires experimentation, and Electron makes it easier to experiment with editor UI. VS Code could become a place to prototype ideas that eventually improve your more efficient editor.