0xcafecafe is right. I think the confusion you're having is "place in line" vs "length of green card process".
Your Indian friends have been waiting 8 years because their turn in line hasn't come yet. The place in line refers to the date of the most recent application that was granted a green card - the date your GC application was filed is known as a "priority date".
For Indian and Chinese nationals with Master's degrees, applications with a priority date of around 2009 are only now receiving green cards. This is the "8 year wait" that your friends are referring to.*
If someone with a priority date circa 2012 were to change their job right now you are correct that they would need to "restart the green card process" at their new job. A new green card application takes between 1 and 2 years. But it doesn't matter because their priority date is at least 3 years away anyway. And the new green card application at their new job can re-use the same 2012 priority date from the old GC application by the previous employer - so they'll receive their green card at the same time as they would by staying at their old employer.
*The only reason this line exists for Indians and Chinese is because green cards are apportioned by the applicants' country of birth, without regard to the population of that country. Since India and China are by far the largest countries in the world, they simply have more applicants than anyone else. Put another way, a Master's degree holder from the Seychelles could get a green card in the same amount of time as a Canadian or an Eritrean or Italian or Brazilian - between 1 and 2 years. I think this whole country of origin business is silly, and not just because it affects me personally. There is a rule change proposed in Congress to address this issue: https://www.congress.gov/bill/115th-congress/house-bill/392