Simple RAW for 5e V: The Disadvantage Strikes Back

[Eriol]

A315 Skills are listed page 174 of the PHB, and include neither initiative nor tools.

Addendum 315: Yes-and to this one. For the OP, note that "proficiencies" such as armor or shields are not the same as skills either, and are also not covered by this spell, but I think that the language around such (like how the "Heavily Armored" feat has some related language) clearly shows that this spell only pertains to skills, and not all forms of proficiency.