The conning tower and its various protrusions is responsible for 50+% of the underwater drag. Add to that the drag produced by the deck gun/s (I don't have that number on the top of my head), and the remainder is the hull form. Bottom line being that the hull form, while important, is not the biggest problem. A reasonable approximation is that battery drain is directly proportional to velocity x drag^3.
One could gain a significant amount of underwater performance simply by the conversion from "conning tower" to "sail" (like the GUPPY conversions); even without elimination of the deck gun. However, snorting significantly reduces speed so it really can't be used to maneuver into attack position; and that is critical for blue-water submarine operations in the Atlantic and Pacific.
During WWII, submerged attacks were a process of detecting a target, moving into attack position (on the surface outside escort detection range), submerge, try for an attack (hoping they don't zig when you want them to zag); rinse and repeat multiple times. Night surface attacks were popular for very good reasons. So, as several have pointed out, the albacore hull does not help in a blue-water approach/attack scenario.
A snorting submarine trades detection range on both sides of the equation (losing as much or more of its own detection range as it takes from the enemy). It's too noisy to use passive sonar plus both visual and radar ranges are significantly reduced. So, patrolling on the snorkel requires significantly more boats to cover any patrol area (or they patrol on the surface).
BTW, the Type XXI was really the forerunner to a revolution in ASW, not ASuW (as some believe) because battery capacity significantly limits the distance it can maneuver against a faster target. How long can that boat (or its more modern cousins) sprint on battery? Probably an hour at full or nearly full charge (which would completely drain the battery). So, while they could use their sprint to obtain favorable geometry during the attack phase, how much distance can they cover and much juice do they have left to operate? If a sprint of 8,000 to 10,000 yards can get you in position for the kill, advantage to the Type XXI (assuming he's got ~80+% charge to start), if not it's back on the surface to reposition. If the boat happens to be in the right spot, great; but outside choke points the "underwater speed advantage" falls precipitously. So relative to u-boats, the Type XXI is probably the best of both worlds for the era as a blue-water ship killer because it retains the surface range, has a "workable" surface speed (against the 10 knot convoys) and has much better ability to escape. An albacore hull would actually detract from that.