my guy it is so much harder. there is so much more than just "clicking really hard". it requires lotsof practice, and with things like block hitting, strafing, w tapping, comboing, using potions, and other things. 1.9 pvp is really bad because you can just hide behind sheilds, and is super gear based. the person with the diamond axe will win, because there is no way you can really do well, the skill ceiling is super low with 1.9, and it's really quite bad. I do like the offhand, but pvp was ruined after 1.9 came out
as a former anarchy server player, they are both easy to cheat on.
also the 20 cps can be done with butterfly clicking. crystals suck so much to play against because that is REALLY gear based. and if you're using crystals, you're probably using a client anyways so it's not fun. pot PVP is pretty cool tho, it does use some good utilities. 1.8 players in my experiance are better tho. it also looks more impressive in 1.8
As I understand it, Old PVP was almost all dependent on Clicks per Second. But there was some strategy and technique behind it. For instance Comboing someone with a combination and knockback and straifing made for some really annoying combos where you would be just out of range of your opponent while he kept attacking you. Also movement speed was very important in pre 1.8. If you were running to a stationary opponent, it would be easier to lock them in a combo. This is also why old PVP usually has a fishing rod, to stun your opponents movement and give you an small opportunity to attack. Lastly bow spamming was a lot more prevalent back then. Shield didn't exist then, and some really annoying player / hackers could do it so fast it was impossible to approach them.
Edit: I forgot to mention sprint canceling or W tapping. This is another technique where you quickly start and cancle a sprint buy rapidly tapping W to amplify knockback.
I personally like the changes to combat as PVP is no longer who hit's more, but who hits better. I know a lot of servers stay on 1.8 because they despise this. I started playing Minecraft in 2014, but I am so use to the change that it's in my muscle memory.
I personally like both but mainly used 1.8 for the majority of my Minecraft experience so I have a preference towards 1.8. A lot of people say 1.8 is spam clicking and mindless, but its a lot more once you investigate and take time to research it. The only thing that annoys me about the newer combat system is shields (kind of) and how slow the "reload" time is. I think both were pretty balanced and it would be a good idea if Minecraft put a setting for what PVP you want a world to have.
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I also don't like the "reload" time and shields. Although once I get good enchants on my armor and sword (yes, I prefer swords to axes even in 1.16), I don't bother with shields and just have a trident glued to my left hand.