MechaPilot
Explorer
Was this meant in a humorous way? Because the OP wasn't asking how to make 5e more like 2e in every way (progression, balance, etc.), he was just asking how to make 5e more lethal, like older editions.
No, it was not meant to be humorous. ASI's contribute to the PCs being able to get through challenges more easily by bumping their bonuses. If you want to make the game more lethal, removing a source of +1s to AC determining stats and HP determining stats and to hit and damage determining stats and save DC determining stats certainly sounds like it would be effective in escalating the lethality (at least to me).
Also, I realize the OP wasn't trying to make 5e run like 2e in every way possible. If I had thought that was the OP's intent, I would have also suggested the following:
Have all caster spells scale by caster level instead of slot level
Multiply the XP requirements for levelling by 1.5 or 2 for caster classes
Allow as the only fighter subclass the champion
etc