In addition to being as strong as a Musketman, the Pike and Shot requires no strategic resources to produce, which makes it an invaluable frontline unit for civilizations without access to Niter. It only costs 10 more Production than a standard Musketman; however, a Musketman will gain a small (+5 Combat Strength) advantage against a Pike and Shot in a face-off. Players who have a large number of Pikemen and enough Gold to upgrade them should do so as soon as the Pike and Shot becomes available, as it will make quick work of Knights and Coursers. It's also a good counter to Cavalry and reasonably effective against Cuirassiers.
The Spanish armies developed a well-rounded defensive tactic after their disastrous experience at the Battle of Seminara. Composed of pikemen and arquebusiers (infantry with early firearms), the unit moved as a cohesive block: pikemen at the center, with groups of arquebusiers surrounding them. Arquebusiers could strike enemies in range, and then fall back behind the “curtain wall” of pikemen when threatened by enemy infantry or cavalry. It worked out well for the Spanish arquebusiers, who could load their notoriously complicated armaments with minimal fear of horse trampling.
- Everything we know about Civilization 6: Rise and Fall - PC Gamer, November 28th 2017