I am by no means a Java coding expert or MineCraft code expert, so I just have to ask: How are dispensers worse for lag than the town farms with billions of animals in them?
While I understand the merit of your point it's entirely misguided.
Whilst towns produce farmed resources to sell, dispensers serve the niche purpose of making machines. Although I love redstone and find the nuances of it fascinating, machinery has little to no effect on the server economy. Furthermore, leather is an extremely important resource required for any sort of caster class, and the other farmed resources have multiple economical purposes.
Dispensers have the purpose of serving only the machine design in which you create them, and often have little effect on the average player's quality of life. That's where your logic is simply misguided.
To further my point, think of it like this. Chests also have storage tiles like dispensers and hoppers, which likely generates lag due to information storage. It's even more likely that chest information may outweigh the lag of hoppers. With that said, chests are a nearly essential part of minecraft and simply cannot be removed, whereas Redstone engineers got by without hoppers before and they can still do it now. (Sucks, I know.). The same applies to your argument about mob farms. Mob farms are necessary to player economy and armor creation whereas dispensers are not.
(My opinion on hoppers and their ban I believe stems from a problem that occurs above a hopper, similar to an item detector or entity detector. I think that the hopper tested for items above it and if positive collected the item. Furthermore, each server tick the hopper would transfer items to another hopper/chest. This would obviously produce lag when large quantities of items are being moved whilst the hopper is doing a detection test ever few ticks. While the lag is usually manageable on normal servers, I believe a combination of the server hardware that Kain has access too, followed by the intensity of Herocraft plugin on the server, creates a strain where the hoppers are simply the last straw that broke the camel's back. This is all theory, though, based on my limited understanding of minecraft logic.)
I'd have to disagree with that statement tbh. There are ICs that aren't in and there isn't a good reason for them not to be.
Example being MC1422 - Mono-stable circuit. It serves a similar function to MC2500 - Pulser only it would likely be less server intensive as fewer checks would need to be made as it has more limited functionality.
I was simply paraphrasing what Xexorian had said about the situation. I'm not on grounds to argue with him about it because I don't have the information on IC abuse because I didn't experiment enough with Craftbook on my personal server to ever know enough about it. Honestly, I would not be surprised if the item Collecter IC causes severe lag due to item check systems (the IC checks for an item, if negative, checks again. If positive, it begins the action. This cycle occurs each tick for the automatic version, and whatever the clock is calculated to on the manual version.)
While there are IC's that I believe have no real reason to be missing from the engineer's repitoiire of tools, I'm not going to debate that topic simply because I don't have any evidence to back my statements.