Strategy - Using Skirmishers
Skirmishers are incredibly effective at early-game defence. Many defensive weaknesses of the Archer are solved by a higher combat strength.
With a higher defensive ability, fewer Skirmishers need to be built to have the same impact as Archers. This allows more focus on development.
Strategy - Against Skirmishers
A Mali player may very well keep off researching Longbowmen longer than other players to focus on building Mints, developing religion (as Mali is a Spiritual religion) or suchlike - Mali's set-up means that they have multiple priorities at this stage of the game. As such, they can be hit while Mali is focusing on more peaceful techs.
Against Skirmishers directly, mounted units can do fairly well due to their higher combat strengths. Promoting Swordsmen in Cover can also be effective.
For Skirmishers in cities, just make sure you have plenty of catapults to weaken cities before overwhelming them. Mali isn't better at crushing stacks than any other nation, so go ahead and send some.