You can still require people to sustain employment in their field. Maybe companies can attest that a particular role classification requires a type of high-end talent. Auditing or otherwise verifying the attestation addresses the current allegations that H1-Bs are given for some jobs not requiring high-end talent.

Having managed people on H1Bs (and therefore been intimately involved with the process) the problems with switching jobs are not the requirements. You’re only allowed to switch to a similar job or a “better” job in a similar line of work.

The problem is that the mechanics of the switching process is extremely cumbersome. Some of the relevant documents are held by your current employer and not with you. The new employer effectively needs to apply for a new application minus the lottery system. There are significant weeks to months worth of delays for the new employers to get approvals, so most H1B employees that transfer are actually working provisionally on the basis of their new approval still being pending. They are very limited in terms of traveling etc during this period. There are significant risks to changing your job when you’re approaching the end of your current H1B visa expiry. This was particularly bad for Chinese applicants who unlike most other nations’s applicants who got 3 year approvals, usually only got 1 year approvals.

The real problem in switching jobs aren’t the policies but the extreme uncertainty and bureaucracy involved in doing so.