I wanted to do an analysis (but lacked a quality dataset or time/willingness to prepare one) that coded mobility differently.

First off, I'd weight countries that grant visa-free access to relatively few other countries (e.g., China, USA, ECOWAS) more than countries that are comparatively more lenient (e.g. countries like Samoa, Tuvalu that grant visa-free access to everyone).

Secondly, I'd additionally weight for residency mobility - the ability to work and live in another country with few conditions (e.g. Schengen area, Common Travel Area, Trans-Tasman Travel Arrangement, MERCOSUR, ECOWAS, CARICOM, Freedom of movement in the Gulf States). Countries like Canada, Japan and Singapore may score well on paper for travel mobility, but are definitely weaker than EU passports that allow you to migrate to where jobs are and improve your own economic outcomes.