Easy hiring/firing of employees may not guarantee a robust economy, but we can see from the situation in Canada, for example, that harder-than-necessary hiring/firing can definitely inhibit an economy that would otherwise be much stronger if it didn't have to deal with such artificial obstruction.
The situation can vary by province, but hiring/firing employees in Canada immediately exposes businesses to significant government-imposed overhead (both administrative and financial) and risk.
Maybe this is somewhat tolerable for larger organizations with dedicated HR and accounting teams, but dealing with all of the unnecessary and pointless government-imposed overhead and risk definitely harms the productivity of smaller organizations. This is especially true for small businesses that may consist of just one entrepreneur, who's also possibly facing tight margins, who'd just like some additional help.
I know of a number of small business operators throughout the country who would love to hire a first employee, or additional employees, but can't justify it due to the overhead and risk that is unnecessarily imposed by government.
I also know of businesses who had hired employees, but eventually had to let them go because the overhead and risk couldn't be justified any longer. Frequent and substantial minimum wage increases can really cause problems, for example, especially when margins are tight to begin with.
Many jobs in Canada are definitely being lost, or not created in the first place, all thanks to government-imposed overhead and risk that supposedly makes workers better off.