True, this is Minmax boards. However, there is optimization, and then there is wishful thinking. Both weapons are on the corner of being so obscure that they are basically unknown, one of a kind items that any DM could ask justification for why you have knowledge of them in the first place (they don't appear in any stories, they aren't detailed in magical item compendiums, your mother, a nice old lady that makes pies on Baker street RIGHT NOW, was not murdered by them, etc, etc). The logic behind stating that you can just find them regardless of setting (which the Hazirawn at least is 100% locked into the Forgotten Realms) is the same logic that states that you can find every single +stat item in the multiverse to give yourself all 30's in your attributes, or infinite simulicri is 100% RAW and will be allowed in every game ever regardless of tone or DM willingness... it can happen, but just like PunPun it is 100% theory in the majority of cases. This makes it viable for theoretical optimization, where there are no limits on anything, but that is hardly the only kind of optimization that exists.
Instead of making a "wish list" group of items, there is also optimization of what you can reasonably expect to find, and working with weaker items to make the most powerful character you can. Making the best Fighter/Barbarian with a +1 greatsword of simple is just as worthy of the title of optimized as the Fighter/Rogue/Ranger one-round nuke'm monster with the +1 Oathbow of Greater Exploding Kittens, a +Enough Belt of Awesome, the ring of Wish and all 30's in every stat. However, one is likely to see play, and one is simply not (though it's fun to see just how many kittens worth of damage you can deal in one round to a fool).
And finally, this being minmax boards and all, I feel it is only right to point out that the bladelock would want the dagger, not the Hazirawn. Greatswords introduce too much MAD into the equation, while the dagger of much fiery buttstabs keeps you straight on the Dex/ Cha stat line that all warlocks have anyway. Far more party-optimal to let your Eldrich Knight fighter, who has more attacks than your warlock (even on the turns where he casts a spell with his action), keep the belt of str so that he can blow fools up and use his greatsword of Bhaal's Essence better than it is to stick it on your warlock so that they can be more competent with it.
(Also... I'll check this, but the Sunlock might actually add their Cha bonus to the dagger's bonus fire damage. One sec... Edit: Nope, just spells. Dang. But it would have been hilarious.)