So, I don't think Google described what senior engineer means to him. Senior engineer means first that you a practitioner and can execute on software projects, but second it means you can influence others. From his own description, I would not be in favor of promotion as there was no evidence of influence. Instead of writing E2E tests, he could of influenced others to write E2E tests and the metric would be the number of diffs where he got people to write E2E tests.

It requires beyond stellar technical work to overlook the influencing aspect.