For starters, Gyojin's are Fisherman who are 1.5x faster and 2x stronger than humans due to the special mucoprotein that is found in the fish which was the cause for this inhuman strength of the Gyojins. From the above it is pretty evident that Gyojins fighting style is greatly based upon Taijutsu prowess.
Being able to create Invisible(?) shockwaves by vibrating the water molecules present in the air is the most important aspect of Gyojin fighting style. Similar the sound release shockwaves, Gyojin's shockwaves are also complemented when using alongside with water techniques.
Other than the shockwaves, Their increased mobility and dexterity in travelling inside a water source makes them formidable. Breathing inside the water source, faster that humans whilst travelling in water, Using water technique without the need for hand seals and resistance upto certain rank water techniques makes the other aspects that supplement the Gyojin fighting style.
Am not sure on what was revamped about the Gyojins but are we able to sense water source? Sense people under water? and what has happened to the x2 Tai boost?
We can sense bodies of water, lakes, oceans, water jutsu, anything inside said water bodies, objects, people, etc. As for the x2 Tai, it's no longer in efect in that manner. It wasn't entirely removed either, it follows two criteria which i'll post later in the hidden group. As for your info, it's correct.
The shockwaves naturally have a highly destructive power, that much is certain. Gyojin produce them through water molecules spread out through the air which also serves a medium to transport said shockwaves into farther distances, however at the same time, passing through the water molecules increases the damage of the shockwave greatly, thus humans and other beings made of water take high levels of damage from them. So in a sense, while the shockwave do not rely on water for strength, it does indeed matter when it comes to increasing it's damange. Because of this, if you shoot a shockwave through a water bullet located infront of you, the shockwave will gain destructive force. But overall it is highly possible that the unstable vibrations of the water molecules have a high role to play in the shockwaves. The fact that we breath and swim underwater is an example of our combat skills, even while underwater. We still swim faster than any humans, akin to a transformed Kisame, and can go everlasting without running out of breath. Further more, because Fishman Karate relies on water to propagate and increase the shockwaves, using FK underwater would make our techniques just as effective and in some cases also increase their power, depending on the technique. We can also, perform regular taijutsu underwater, as our mobility is not hindered, we are after all, fishmen. Although, keep in mind that using a taijutsu technique which uses fire would result in complete failure underwater, logic and reason still applies down there after all.