H1B visas don't require employers to post jobs; this PERM process comes later when someone seeks an employment sponsored green card.

Visas could be allocated in some kind of priority order, but salary alone would probably concentrate visas to just the relatively high-paying tech sector, leaving other professions out entirely.

I'm not sure that's good; the US also needs people with expertise in science, industrial and agricultural control systems, clean power, and more. But these professions tend to earn a fraction of what a software developer makes. Other countries have gone with points systems that try to balance for this.