Does increasing aptitude per level make a difference?

Solution 1:

The aptitudes will increase by the same amount from being promoted as if you'd made a new character in the next tier, so that won't make a difference in the end. However, you won't have higher base stats like a character that started at a higher tier, so a character promoted from tier 1 to 6 will be weaker than a new character you started at tier 6. This is explained in this thread:

When Promoting automatically, a character gets their Aptitudes increased to match the new tier, but their base stats aren't recalculated, and base stats factor into stat growths, so a character that started at Tier 6 will be stronger than a character that started at Tier 1 and ranked up to Tier 6.