Didn't realize Mobile had a way to get Drax pre-hardmode. I learn a lot from forum posts.
Dizelvink, my latest 1.3 character, finally got around to fishing up a Reaver Shark. It's a considerable improvement but doesn't make him a super fighter. It does mean less time spent (or wasted, depending on one's point of view) chopping holes in the ground, leaving more time for the interesting parts, the fun parts of the game: exploring, collecting, fighting, and building. I can't see any drawback to this.
He also fished up a Sawtooth Shark and a Rockfish, providing a triad of decently high-powered toolfishes. I don't find the abilities to slope blocks more quickly, or to harvest wood in a less yawn-provoking way, to be in any way harming game balance. Having gone through early game stages several times, I feel sufficiently familiar with what it's like to be a sloooow worker — I've no wish to continue at a molasses-in-January pace longer than necessary.
Now, if it were possible to get, say, Shroomite Digging Claws from a naturally spawning Glowing Mushroom Chest in pre-hardmode, I would definitely consider that innovation ripe for nerfing. In fact, I'd recommend gating it behind the mech bosses. The Claws' speed is undeniably breathtaking, to the point that I wouldn't consider it hyperbolic to say pre-hardmode availability would be unbalancing. Saying the same thing about the Reaver Shark… I would.