Since there are more enemies, your dwarves will also get more EXP on higher battles. So new dwarves will level pretty quickly, but only the veteran dwarves will be able to achieve high WISDOM by drinking beer from an early battle on. This is actually intended design.
Also, 'Tome of Insight' can help new dwarves catch up faster.
Balancing is of course always ongoing and I will keep an eye on this, but currently there are no changes planned for the levelling process.
Thanks for playing and getting this far!