It's hard to tell if a game's combat system is a make-or-break factor for its financial success. An RPG should be more than just the sum of its parts. What killed PoE for me was the lack of an engaging narrative and scarcity of interesting characters.
The developers of the PoE series were apparently scrambling and looking for answers as to why PoE 2 was severely underperforming. They subsequently tried to "fix" the game by slapping on a turn-based mode and hoped for a resurgence... It changed nothing, because the true problem is the game/series in its entirety.
Turn-based combat also did nothing for Torment: Tides of Numenera. The game still flopped really hard.