Even as a fan of the show, I agree on this point.
I don't want to get too into the quality comparisons between Supergirl and Gotham, since this is the ratings thread, but from a ratings perspective I definitely think Gotham is on firmer footing at this point in time. The ratings appear to have stabilized at around 1.5 give or take a tenth a point, whereas Supergirl is still dropping. Plus Gotham is on the weaker network and is well ahead of several other competing shows on Fox. Gotham seems very likely to get renewed for next season, whereas I would consider Supergirl a true tossup at this point.