https://visaguide.world/us-visa/nonimmigrant/employment/h1b/...
Though the expected norm nowadays is for it to be a cheaper second-rate labour supply restricted by years long waiting lists and lotteries, and not a smooth pipeline of geniuses and super-geniuses interested in emigrating to the US,
The other employer still needs to be willing to sponsor you, and that's often not the case.
Yes
> can start working immediately
Abso-lutely not. Check out Reddit to look for accounts of how the transfer works and see how easy it really is...
When you transfer, you need a lot of cooperation from the new firm as they have to be ok filing paperwork, they have to do it in a timely fashion, and due to processing delays on the order of weeks (if all goes well) you cannot start work immediately. For many, many employers, this puts you at a strong disadvantage against applicants who are all good to go and ready to show up for work on Monday.
This thread is talking about, from employee's perspective, it is hard to jump ship.
The original ideal and present situation seems fairly clearly spelled out in an unbiased manner.