I don't believe in that statement, if Real Madrid want to be even better next season then they have to bring in more players because this season they were left behind by some of their main players and even now there are many old players at Real Madrid whose quality has decreased.
The position of attacker and defender is Real Madrid's weak point next season and if the current transfer market does not buy the players needed in these positions, then Real Madrid's strength will not be much different from the previous season. For the midfield position they have Bellingham as a new force that can help Real Madrid and I think that position is safe for them next season.
The positions of attackers and defenders at Real Madrid have been weak for the past two seasons and last season Madrid also did not fix the weaknesses in that position, making it easy for them to get knocked out when playing in the Champions League.
For La Liga itself, Madrid is strong enough and able to compete with all the teams there, but Madrid's goal is not only La Liga, but also other truly prestigious leagues such as the Champions League.
The transfer season is not far away and the games will start at the start of the summer so if Madrid don't make a move soon I'm sure they will stay the same in that they will only win the Domestic League.
The transfer window will still be open and still a little long to close, so it's only natural that Real Madrid won't be in too much of a hurry. Also, buying a lot of players is not right if the end result is not a good performance for the team. So, buying only a few players but having a great chance to contribute well to the team, then of course it's the right choice. Also, the new season was still quite a while away from starting for at least a little more than a month, so they didn't need to rush things.