I'm using a base-spec M1 MacBook Air since a year or so now. I have a 4K external monitor attached most of the time, usually four windows in Safari with perhaps 100 tabs in total, Mail, a bunch of terminals, Slack, Signal and Telegram open. It's snappy all the time, and consistently feels much much faster than my previous laptop which was a maxed-out Intel 13" MacBook Pro.
The only thing that ever makes it sluggish is if I open VSCode with a large workspace. Even with all plugins disabled. No idea why. I just stopped using VSCode.
Safari might be the big difference here, and you only really have one Electron/Chromium app, Slack, and it's generally better than others about managing its resource usage.
Yup, I switched back to Safari because I noticed Firefox uses significantly more energy (battery lasts a few hours less when I'm out). So it's likely that it has an impact on responsiveness too.
The only thing that ever makes it sluggish is if I open VSCode with a large workspace. Even with all plugins disabled. No idea why. I just stopped using VSCode.