Salwyrr isn't a hacked client. I agree, but It was a hacked client. The developers didnt knew shit when making this client. See famous youtuber Tenebrous's video talking about unknown clients. He states that Salwyrr has no-slowdown when block hitting, but the devs claim it to be a bug. But if you ever used Salwyrr before their 3rd update, you can block your sword in 1.9+ versions too, gaining a pvp advantage over other 1.9+ players.
Secondly, Toggle Sneak. This client has toggle sneak, toggle walk, toggle sprint etc. But their toggle sneak, and toggle sprint was bugged before their 3rd update. What I meant is, in vanilla Minecraft, we cannot open Chests, Barrels, interact with anvil, crafting table etc., while sneaking, but allows to place blocks on their faces. But this client had a bug which made them interact with these things even when they had ''toggle sneak and toggle sprint on''. They also stated that, the developer of Salwyrr asked the developers of Lunar to make Salwyrr right, so that the client does not violate their rules. (Got these info from both Lunarnetwork/Hypixel forums). This also states that the developers aren't skilled enough to make it a good client.
A problem which I experienced myself : We cannot break blocks in Lunar, Badlion, Laby(I took these clients as an example cz they are one of the most trusted clients out there)while blocking the sword. But in Salwyrr, we could easily break a block while the sword is being blocked. Hold LMB and RMB on a block in 1.8.9 and it may not show animation of breaking it/the animation restarts at 99% on Laby, Lunar etc.
Before these 3 bugs were cleaned, Hypixel blacklisted Salwyrr only for these 3 bugs, which is basically a disallowed
modification there. (Hypixel currectly allows Salwyrr, still worries about the mistakes in the client tho)
!!!! Now, who would play in a client that has tons of bugs. These type of clients must be blacklisted on every servers, even on
cracked. Who knows, if these bugs still exists. !!!!