I don't play warlocks but I have seen the unpredictability. Oddly, in town they seem to be powerhouses, recovering their spells over a leisurely meal or at a tavern (which might currently be smoldering). While out in the wilds, you spend huge amounts of time on edge waiting for traps and ambushes, creeping at a snail's pace through an area of two or three city blocks, hoarding spells like a miser.
It is incredibly swingy, especially if the gm runs one adventure path in town and another in the wilderness, as the different authors create significantly different play styles, with GM adding possibly a 3rd.
Based on what I have seen, split the difference.
Give the warlock regular, old spell slots at 1st & 2nd level. At 3rd they get Pact magic. They would start at 1 pact slot and max out at 3. Pact spells known would be 3 less. At 3rd+ warlock, they would know 5 1st level spells (3x spells from Warlock 1st & 2nd plus 2x 1st from Patron).
Now they have a pool of basic slots for utility spells (hex, shield, detect magic, etc ) and still have some short-rest nova.