At least in Germany, such agreements are afaik invalid and without a severability clause, possibly all others too. Simply because something like copyright cannot be assigned in Germany. Secondly, there are ways to use Reddit without ever having agreed to the ToS.
That clause does not assign copyright. You explicitly keep your own copyright (in the previous clause, I didn't reproduce it above). You just grant them a license to use your content in the ways they listed.
In Germany lopsided contracts clauses that surrender all rights are void. GDPR also gives you the right to recall all your data, so you should be able to delete your account and all your data.
