The user you replied to is against Roblox forcing others to use third party platforms, not Roblox restricting others from communicating with off-site platforms as what your post implies.
People often use the argument “anyone allowed to use DevForum should also be allowed to use Discord” while debating this issue, and while this claim is correct in some way regarding the minimum age to use these services, you also need to understand that the Roblox developer base is extremely diverse.
On this website, you can communicate with people from all different parts of the world, which also means you will find people coming from different household environments with different family rules and customs. There are many reasons why a parent would rather let their kid use a heavily moderated development forum with around 100,000 active users a month compared to a much less moderated social platform being more than a thousand times bigger with 140 million monthly active users. Not to mention that Roblox development is extremely educational and really helps kids and teenagers prepare for the real world — parents could allow their child to use DevForum for this reason, while holding back on Discord for safety concerns.
Now back to my statement about the community being diverse, developers willing to hire someone should be prepared to encounter someone who has different family rules and is not permitted to use Discord. I also believe that anyone who is willing to find a job should be prepared by having Discord because it is the communication norm.
Onto the chat filter issue, while I do believe Roblox should definitely loosen up the chat filter on the Talent Hub, Roblox should not force users to use third party platforms as an excuse for not wanting to fix the chat filter. Imagine this fake situation of Twitter trying to target kids and implementing extreme moderation and deleting any post that does not pass its faulty filter, while telling its older user base to use a different platform to post totally appropriate things without it getting incorrectly blocked. Instead of forcing everyone to use Discord, Roblox should fix its chat filter, and recommend Discord for easier and more mature conversation. This benefits everyone, regardless of being able to use Discord or not, and contrary to your reply, it does not ban anyone from using or talking about using off-site platforms.
I will conclude with this: I would certainly recommend Discord for users in the collaboration field, because it makes communication much easier, but if you run into someone who does not have access to Discord, be prepared to use alternatives such as DevForum PMs — it’s just a part of working with people with different household rules.