You can look at almost every big decision they have made from past nerfs to MSQ duties to job changes on all roles as a reflection of engagement metrics.
Steps of Faith nerf - Users getting barred by it
ARR MSQ nerf - User falloff before HW
Healer Kit nerf - Lack of active healers in PF, biggest complaint being "too complex"
Ast specifically, gets tweaked every expansion and for some time was the lowest played Healer.
Eureka nerf - less people in the instance, laxed requirements to proceed
Bozja nerf - see above
Engagement is superior for any company. It directly transfers to wealth. If your player engagement is low, people fall off, thus less money. Business 101
/thread- People literally saying they are leaving cause they don't find the specific content engaging enough.
Now you can cut the pie into categories to further analyze engagement metrics within certain domains, for example, savage content, understanding what types of mechanics and overall balance within encounters see the most clear rates tier for tier or understanding which classes are specifically popular over others vs the design of a particular encounter.
Same with something like crafting, being non-macroable in HW and how many crafters participated in that vs current last 5 years where all crafting is macroable and easily accessible. Notice they never went back to HW style crafting by and large, outside of a sprinkle for ishgard restoration. Metrics (and how that relates to their overall goal) matters most.
To say otherwise is folly. SE is a company first and foremost. They are always looking at numbers. When they make content for a particular base, say casuals and MSQ, they definitely are looking at how many people are proceeding through it and if/where there is fall off. If it's specifically jarring enough, they tend to employ a fix somewhere.