I am quite happy do ditch the replay required rule. Most of the stuff worth discussing is far too complex for showing it in one replay. We are not asking, is the pillar too weak against the ishie in a mass for mass confrontation. We are asking: Is the t2 stage too short, are ras bois op, is the repay time of the t3 mex too short and if so how would we fix it. The problem is that be best data we have is just the intuition of experienced players that have a long discussion which hopefully leads to a consensus.
So how do we put a barrier into place that prevents the balance forums becoming a gameplay and training channel people. One suggestion would be requirering 1500+ global rating in order to start a thread, as a minimum requirenment for game experience/knowledge. Wich I would consider problematic in the way that we already have quite a rating hirachy. People respect each other too much because of their rating. If you were a lower player and really discovered a worthwile issue it wouldn't completely shut you out of the balance discussion. You would have to convince someone 1500+ to make your point for you. That would offload a lot of the garbage filtering to the playerbase.
Another option would be that a new balance thread is locked until approval by moderation, or the balance team. Also I think balance discussions should be moderated very hard. So the information density of the discussion is high enough to be worthwile reading. If you just want to rant about balance do it on discord.