>adds input lag
A lot of shmups and arcade games actually may have input lag by default, see battle garegga: has 3 frames of input lag if I recall, so really they're just accurately emulating the games and also accurately emulating how bad you suck on a real machine :^), a lot of modern arcade games are just pcs, see the taito arcade machines (games like Chaos Breaker / Dark Awake), just a embedded windows machine with low spec hardware.
Anyways, if you're trying to get good, abuse savestates, I don't care about the 'cheater' aspect or the nips didn't have this, it will accelerate your skill way faster, when you feel like you can 1cc, keep playing over and over without savestates and get used to being close to dying a lot, doing actual runs and learn to recover from bad plays in middle or near the end of your run.