This is nothing new. The problems with work visas in the US are:
1. Cheap bodyshops consuming much of the quota; and
2. Immigration being tied to an employer.
(2) is a direct cause of (1).
For those that don't know, sponsorship for a green card basically involves two stages.
Labor Certification ("LC") is the first and most time-consuming stage. It involves "proving" you can't find a US citizen to fill the job. There is then a queue with a quota system based on country of _birth_ (not citizenship). For countries with a high number of immigrants (eg Mexico, Phillipines, India, China), the queue can be _years_ long. During that time the employee is essentially an indentured servant. Employers can and do exploit this situation.
The Department of Labor can add to this by randomly auditing a particular application, which will add a minimum of 1-2 years to the process. Sometimes this is for cause but the DoL's stated policy is to prevent petitioners from "gaming" the system so they disguise their auditing criteria by randomly selecting applications to audit.
The second stage is basically a formality: filing for adjustment of status.
So for a period of 10 years or more the employee may be in no position to leave, no position to negotiate and will quite possibly have to work under abominable conditions for substandard wages.
The LC process ostensibly has a prevailing wage determination step to ensure the employee isn't being victimized. Trust me, it's a joke.
Startups here, as a general rule, aren't the problem. These nameless bodyshops paying $50,000/year or less for a warm body to contract out to a Fortune 500 company for $500/hour are.
If you kept the current green card quotas and simply made H1B visas portable and immigration essentially automatic when your number (in the queue) is up then you'd end a lot of these problems.