The solo content isn't really affecting this. Even if you make it so all healer & tank attacks only have 10 potency or decrease the dps needed to clear dungeons/raids, everyone would still be spamming their attacks as much as possible while only using just enough healing/mitigation to keep everyone alive; Because more dps = faster fights and faster fights = less opportunities to make mistakes/ larger buffer to not fail fights due to mistakes.

Only way I see how you could change this is by forcing players into situations where they can't dps; But at that point, you're changing how dungeons & raids work in FF14