I went through the discussion area to see what things you were talking about, as well as dm history, and I thought I answered your questions but apparently haven't, so here it goes:
Sniper increases the speed of projectiles being fired out of bows. In the vanilla Minecraft code, the damage of a projectile (esp. the arrows shot out of a bow) are directly proportional to the speed. This can also be figured out through the Minecraft wiki (
https://minecraft.gamepedia.com/Bow#Weapon): "The damage can be less than the maximum damage if the arrow slows down after being shot." Therefore, increasing the speed of the projectile will make the arrow damage them more. If you would like a fix for this error, have Sniper and Power be conflicting enchantments so their damage multipliers won't stack.
For your opinion about having the items lower the levels for the player, that will be a no because there are too many variables in play with that kind of system to not introduce more bugs into the system. Creating your own plugin that could do this, or asking someone else to make that for you, will take less than an hour, as the code is open-sourced anyway.
As for your message about spike lags while using the plugin, 1. I am not a full time developer. I do this in my off time because I think it's fun. 2. Before developing this plugin, I have never seen server timings posted in full, and no one has explained to me how to read them or what they mean, so I can only do so much with them. 3. I never received updated timings from you to continue optimizing the plugin. Minecraft is a very unoptimized game as it currently is, and like I said before, I'm not a full-time developer, there is going to be parts of the code that get better over time, and some that get worse. I don't run a server that has large amounts of players where I can sufficiently understand where issues come from. The only reason I have a featured server is because the owner of that server helps me bug fix these versions, plus gives me a huge amount of ideas and helpful tips.
I try to answer everyone in the discussion area, but unfortunately, as I only do this as one person and for fun, some things get overlooked sometimes. I'm very sorry for not answering your questions in a timely fashion, and I hope this can answer a lot of your points. If you would still like to use the plugin, sending me a friend request on discord (crashtheparty#3356) is a much better way to get support for general issues, or sending a bug report over to the github (
https://github.com/crashtheparty/EnchantmentSolution/issues) as I double check those every once in a while and make sure if there's an answer for one, that I will answer it.