If you make a list of all the commanders you are facing, like I did over the last couple months, you'll see that there are over 800 different commanders fielded in Brawl. And every day my list grows longer.

But, some commanders are really overrepresented. The top ten in my 3100 games right now are:

1,52% Giada, Font of Hope
1,42% Jodah, the Unifier
1,35% Hei Bai, Forest Guardian
1,35% Sephiroth, Fabled SOLDIER
1,00% Etali, Primasl Conqueror
0,97% Kotis, the Fangkeeper
0,97% Ureni of the Unwritten
0,90% The First Sliver
0,87% High Perfect Morcant
0,87% Pantlaza, Sun-Favored

which together make up 11,23% of all those games. So about 1 in 9 matches is against one of the top 10 played commanders.

Maralen checks in at 12th place with currently 0,81%. So yes, she comes up very often as well.