Go to https://jsspeccy.zxdemo.org/, and start up the spectrum emulator.
Choose '48 BASIC'.
Once the emulated speccy boots up (oh, yeah - notice you have to wait for a noticeable delay while it initializes all 48K of RAM there...), press and hold down the 'C' key. It should start typing:
CONTINUE CONTINUE CONTINUE CONTINUE CONTINUE ...
Within a couple of seconds, the input latency will have become noticeable.
After about half a screen is filled up with CONTINUEs you can take your finger off the keyboard, and it will keep slowly typing CONTINUEs for a second or so more. Now try typing some letters. Feel that delay between your input and the character appearing on the screen?
I can attest from personal experience that this is an accurate and faithful emulation of exactly how a 48K Spectrum behaved.
There was no golden age where computers were instant and always responsive. Floppy disks chugging away while little watches and hourglasses replaced your mouse pointer were the norm throughout the pre-internet era. On a terminal connected to a minicomputer, you could watch the text come in character by character on your terminal.