Why on earth would you bother using a regular +1 weapon if you could have an improved pact weapon? It's the normal +1 weapon that is rendered useless by improved pact weapon, not the other way around.
Because one has build cost associated with it, the other does not? It's +1 Magic Weapon + diffrent Eldricht Invocation or +1 Pact Weapon. One is clearly better than the other. Not to mention that weapons with higher bonuses exist.
Thirsting Blade is a level 5 invocation... I don't know where you're getting level 12 from.
My mind swapped Thirsting Blade with Lifedrinker.
