Will you rate the other invocations soon (cloak of flies and the likes)? I really like your work so far btw.
PS : The way Improved Pact Weapon is worded , RaW wise, it seems to me that you should keep it even if you get a magic weapon since it allows the benefits of Eldritch smite and Lifedrinker on the Eldritch Blast cantrip (never once is it worded as "melee weapon hit/attack" ; they all use the idea that you need to hit with the weapon and said weapon is treated as your focus via IPW, hence "hiting with it").
An arcane focus is a substitute for a material component which in of itself is one of possibly three parts to casting a spell. You don't hit someone with your arcane focus when you cast a spell anymore than you hit someone with powdered rhubarb and an adders stomach when you cast Melf's Acid Arrow without a focus. You could just as well argue that you are "hitting" you target with the verbal or somatic components of the spell (*)
If this was intended then you'd have always been able to do it using a quarterstaff as an arcane focus without IPW
Note Eldritch Blast is a VS spell so you don't use an arcane focus when casting it anyway.
(*) the SCAG cantrips are an exception in that the material component is specifically a weapon that you hit someone with.