MIRC is not a freeware program, and if a customer asks for something that makes sense, I don't understand why it's not already done.
This is a weird argument. Are you really suggesting that because you paid for mIRC you have the right to *demand* that every feature you want be implemented? Sorry sir, that's not how paying for things works. You paid for mIRC as it was at version X, not as it would be from now on. mIRC is not run by a public company, and buying the product does not make you a shareholder. Khaled implements the features that are feasible, have actual user support, and cannot be implemented by other means. So far there has been little user support and ample alternatives. Also keep in mind that Khaled can only do so much. He has already mentioned that it's on his todo list. The existence of reasonably usable scripts makes this a fairly low priority issue IMO.
A full test done by 10 different users around the world using 2 mirc's
Great. Where are the results of this test? Specifically, what is your metric on "heavy traffic load"? What is your metric on "make us all sick"? What script were you using? Did you try *ALL* available scripts? If you had actual results, you might be able to make a case. Frankly, my observation to your hypothetical results is that, if the script you tested was slow, the script is pretty poor. An encryption/decryption script is not computationally expensive enough to cause any kind of significant lag/delay. Or in other words, there exist performant FiSH implementations-- it's certainly not impossible to do.
Then why are there so many of them? And why are there so many users using them without issue? Do you speak for every user?