A top Engineer will go to a company which aligns with his personal and professional goals. With your example, no one would have created a startup and simply working for someone who pays more.
Trust me on that I am working with GitLab from past 6 months and I have never regretted a day. GitLab is always open for ideas and this is also work in progress. How many companies have you seen declaring their compensation framework :)
Knowing Ruby is not a strict requirement for all the positions https://about.gitlab.com/jobs/. But for few it will be great if you know any scripting language and just basics of ruby.
It only happens in dreamland :) option (4). In practical, its a human tendency that after some time either we get irritated by each other or we start finding flaws in any decision taken by the management or vice versa.