They are most likely only looking at the RAM used but the 'Discord' process, which is just the native launcher code and OS hooks (on MacOS here, may be different on other OSes). The electron processes are called 'Discord Helper' and will be using quite a bit more RAM, though I still wouldn't consider it 'heavy'. The same process structure is true of Slack as well (maybe all electron apps, I'm not familiar enough to say).

Both Slack / Discord use around 400MB including all processes on my machine, tho it certainly varies with what is on screen. In comparison to the gmail tab I have open in Safari that is using 1GB, 400MB isn't bad.

400 MB is enough to run Mail and Messages with room to spare.

The Facebook Messenger tab in my browser consumes way more memory than that if left open.

Heck my Digital Ocean dashboard tab is consuming 155MB of memory right now (WTF DO?)

That said, I am blown away whenever I install an "old school" native Win32 app. The 90s APIs may have sucked to program for, but the end results stood the test of time.

Exactly, look at the "system" requirements for AOL Instant Messenger:

Windows 2000 or higher Internet Explorer 6.0 or higher 128MB RAM/512MB for enhanced multimedia features (TOTAL RAM in the system!!!!!) Macromedia Flash Microphone and speakers/headset for voice/audio chat

It takes about 0.5 GB for me as well, but shared across three processes (main app and two "helpers"). Maybe parent commenter looked only at the main app's usage?

Could be, but I just checked again and the App takes ~29MB, and the two background processes take ~24 and ~136 for a total under 190MB. Whether it uses 1.5% or 4% of my RAM is meh either way in this case. Windows 10