I think at lower levels, it seems like the red cons are considerably harder than blue white or yellow cons. But, as you level up, it gets easier and easier to take on red cons.
I think this could probably be adjusted by messing with your NPC's accuracy and attack stats in the NPC_Types table. Since accuracy and attack should decide how often and for how hard on average that a player with X amount of defense (and defense skill) should be hit, you should be able to adjust them so that it scales up better than you are seeing.
The only problem I am having with that is finding the appropriate settings for those stats to make them scale the way I would like.
I made a tool request in the post below to help find all of this information and KLS provided a nice little spreadsheet that actually seems useful for this. But, I imagine a tool could be written to make it more accurate and easy to create NPC stats to be balanced the way you want.
http://www.eqemulator.net/forums/showthread.php?t=24671