If any check was implemented it should be a main stat check, because it would put emphasis on keeping people's left side gear and weapon updated and would also prevent people from using the wrong type of accessories to enter dungeons. Item levels imply power but measuring power directly is more accurate.

These requirements probably shouldn't be too strict so that people can still enter leveling content with the jobs they intend to level without having to spend hundreds of thousands of gil on temporary leveling gear.