It very much is average for a d10 is 5.5, agonizing gives +5 with 20 charisma averaging to an extra d10 worth. . The dmg 284 table has:
1st 1d10
2nd 2d10 Level 1-4 agonizing blast is here (1d10+an effective second 1d10)
3rd 3d10 add repelling & you probably get here for a 5 foot knockback on top
4th 4d10 Level 5-10 agonizing blast is here. (2d10+an effective second 2d10)
5th 5d10 add repelling & you probably get here for a 10 foot knockback on top
6th 6d10 Level 11-16 agonizing blast is here. (3d10+an effective second 3d10)
7th 11d10 add repelling & you probably get here for a 15 foot knockback on top
8th 12d10 Level 17+agonizing blast is here. (4d10+an effective second 4d10)
9th 15d10 add repelling & you probably get here for a 20 foot knockback on top
Eldritch blast is very much not the equivalent to a heavy crossbow because a heavy crossbow has the loading property, does not deal force damage, does not have a knockback, & does not scale the fighter extra attack based on character level like EB.
That's a lot of ifs balanced around "your the gm, you fix it & you figure out where it needs to be & you make it work" piled on a GM by d&d5e. With the system structured mechanically to almost guarantee that players can successfully rest without gm fiat simply disallowing it things are almost certain to swing in a direction where short rest classes are problematically overly good