"Hardmode" is just a fancy name for blocking all 3rd party scripts, which there aren't even any to block here in the first place. What does happen is that two of the three Discord domains get flagged and blocked:
One is Discord.gg which is the Websocket to get and sent events, so it's needed for functionality.
The other is Discordapp.net which is pretty much their media server.
If you block all 3rd party scripts, frames and connections, then yes, your number of blocked items will shoot up into the hundreds. But if you knew what you are doing and just took a look at what was actually blocked, you would realise that it all was just requests for media and profile pictures. Even with fully enabled hardmode, there wasn't a single request from a 3rd party advertiser or data broker, not even Google.
Your arrogance for using hardmode is completely unfounded if you don't even know what it really is blocking. All you are doing is looking at a number go up and are patting yourself on the back for it.
If there is any benefit to it depends on how discord sells your data.
The baseline assumption is that they just collect and sell everything as is, considering how shitty their privacy policy is and the general track record of corps following gdpr guidelins. With that barely anything changes.
If we belive the claims in their policies, then things get a lot better. Only aggregated and anonymized information is shared for marketing. Apart from that only their direct partners get more personalised information. Sadly, Google will probably get a lot of it since they are one of Discords cloud service providers but it should still be less then them collecting it themselves.
Now if we also assume they are following all GDPR laws, than even Google should only get very restricted information about you needed for their services.
What they really do with your data is anyones guess. I assume its somewhere between 1 and 2, but there is no proof I know of. The only benefit I really see is that it's a lot easier to just block the one Discord API instead of 500 individual brokers.