Hello, My Dear SplinterMates,
I, hope you all are doing fine and taking good care of yourself.
Incase; I get stuck anywhere with any question, I'll make sure that I reach out to the SplinterLands team and have that question answered.
The short answer is that - You will not be able to play with monsters card at their Max level by Just Maxing Your Summoner Cards. This implies that you will also at the same time need to Max your Monster Cards as well if you want them to play at Max Level - when Your Summoner is at Max Level...
Looks confusing right?
I've gone ahead in explaining - how the Max Level Cards work along with their stats as mention in the image.