It seems strange that you can download and use Hyper on macOS, because it seems to be windows only.
General Performance of iTerm
The FAQ from iTerms website suggests this:
Disable transparency and blur. Use a solid background color rather than an image.
You might also want to look into how many Triggers you have activated, as they are known to decrease performance. You can find these in
Settings -> Profiles -> Advanced -> Triggers.
Pasting Performance in iTerm
I couldn't replicate your issue on my computer with this short text, but making it about 20 times longer the same happens here. My guess is that iTerm thinks that you are typing and redraws the whole text every time it sees a new character. The same happens on vim in macOS and Ubuntu (see here enter link description here)
Fixing Pasting Performance in iTerm
There does not seem to be an easy fix for these performance problems. If the FAQ did not help I suggest to use this command:
pbpaste >> test.sh && chmod +x test.sh && ./test.sh && rm test.sh
pbpaste accesses the clipboard (try pbpaste on its own) and >> test.sh writes it into the file test.sh. chmod+x test.sh will allow test.sh to be run from the terminal, ./test.sh runs it and rm test.sh will remove all files called test.sh. This works exactly the same as pasting it but without the performance decrease actually pasting it brings