If the attack is using a spell attack modifier and the PC is building DEX instead then the attack does less damage and also hits less often.
Starting with a 14 DEX is still only 1 point in AC behind. The rogue in armor has a 14 AC instead of a 15 AC. But by using the Sage background for the Magic Initiate feat the rogue can skip the armor completely for Mage Armor and still have that 15 AC too that the High Elf did not supply.
If the build is focused on INT/whatever asap and then DEX the Sage can to that. 10 STR, 15 DEX, 14 CON, 12 INT, 16 WIS, 8 CHA based on standard array.