Questions Regarding H1B Visa

[trengsoba]

I had the following questions relating to the H1B Visa:-

1. Are you often left at the mercy of the employer because they sponsor your visa (unlike EU where employers don't have to sponsor your visa)
2. Will you likely only get H1B visas and renewals if you're from CS?
3. How much time does the renewal process take?
4. Does renewing the visa every three years pose a lot of uncertainty/ hinder your ability to switch jobs?

Any advice is greatly appreciated!