Nobody said Courtois was bad because it was very clear that in terms of goalkeeping at Real Madrid, Courtois deserved a lot of appreciation because his saves were extraordinary, but it would be very complete if Real Madrid's defensive line became stronger again. So a goalkeeper like Courtois won't be too tired in saving a ball shot at goal directly.
Courtois has played 36/38 games this season in Laliga, meaning he has missed just 2 games all season. Real Madrid have only conceded 31 goals this season or 1 more than Sevilla. So it may be true that Real Madrid have had good goalkeepers this season but they are not good enough defensively.
Next season he may still be Real Madrid's first choice in various competitions, but to be honest he will turn 31 next season. If Courtois is able to maintain his form then I believe he will be irreplaceable at Real Madrid in a few more seasons even though he is already over 30 years old.