>>3781745 (OP)The Prince of Cannock has a lower level cap than the Prince of Midenhall, but takes the same amount of EXP to get to max level, so he levels more slowly. The Princess has an even lower level cap and will level even more slowly.
Prince of Midenhall takes 2800 EXP to reach level 10
Prince of Cannock takes 4000 EXP to reach level 10
Princess of Moonbrooke takes 12,000 EXP to reach level 10
It's unusual but they did it this way because it was their first game with multiple party members and they wanted each character to start at level 1. The levels aren't supposed to be equivalent, the Prince of Cannock is "supposed" to have better levels than the Prince of Midenhall. It's made this way so that you can use your characters as soon as you get them, instead of later characters starting as weak level 1s who have to be grinded all the way up. For example, Princess of Moonbrooke starts with 28HP like the Prince of Midenhall, even though you meet her much later so your Prince will have much more HP when you recruit her, but it's balanced fine because she's supposed to have less HP as a spellcaster and the enemies you'll face after recruiting her give more EXP than the starting enemies.
All of this is 'in theory", but in practice, the Prince of Cannock tends to be your weakest character, not because he levels slower but just because he wasn't balanced well.