Lot of people undermined Madrid with their squad in CL and LaLiga last season too but they came out as a winner but they showed great spirit and became champions of both. Madrid are strong candidates in my opinion. Barca are also a strong candidates but I have my slight doubts still.
It was this doubt that motivated the Real Madrid players last season by beating their opponents in the UCL by becoming champions last season and Real Madrid also winning Laliga. that was a really great thing for them in the previous season. for the upcoming season Real Madrid are still a strong enough candidate in the UCL competition or in the domestic league so that other teams may find it difficult to beat them.
Actually for La Liga there is no doubt whatsoever for them to become champions even though they were underestimated in the UCL last season because apart from facing strong opponents they are also not as well seeded as other clubs, especially for big clubs and maybe this season will also be like that in UCL. But indeed as you said, this could be one more motivation that can be used for Madrid to go beyond the imagination of football fans.