Adding optical elements that are not part of the original lens design almost always introduces additional optical errors due to some degree of "mismatch." Image quality is (almost?) always reduced to some degree (but the benefits can outweigh that negative).

Reducing the magnification/increasing the FOV can increase apparent image quality by reducing the apparent movement (camera/subject). And reducing the FOV can increase image quality by requiring the camera to be closer to the subject, which makes the details larger/clearer to start with. But those two things counter each other... moving closer inherently increases the effective magnification.

Adding optical elements that are not part of the original lens design almost always introduces additional optical errors due to some degree of "mismatch." Image quality is (almost?) always reduced to some degree (but the benefits can outweigh that negative).

Reducing the magnification/increasing the FOV can increase apparent image quality by reducing the apparent movement (camera/subject). And increasing the FOV can increase image quality by requiring the camera to be closer to the subject (for a given composition), which makes the details larger/clearer to start with. But those two things counter each other... moving closer inherently increases the effective magnification.