Arguing the semantics of whether or not a houserule in a game you play in counts as "your house rule" is a bit too off-topic, so I'll focus on the second part of your post.
At this point, I'm arguing for balance between the classes rather than a return to something closer to 5e RAW. And the presence of magic items that synergize with certain classes is definitely important for that.
if you're gonna base your argument on some sort of class balance thing, I don't see how rogue sneak attack needs beefing up in terms of it being too wimpy compared to other class abilities. it's a pretty strong ability as is. And letting it work with d10/d12 2-H weapons doesn't make it all that much stronger (setting aside GWF for the moment).
That's missing the forest for the trees: considering sneak attack in a vacuum and as a singular ability compared to other single abilities.
OP asked for sneak attack to be usable with all weapons. This is strictly a buff to primarily rogues and multiclassed martials. My (partly facetious, admittedly) argument is that: since casters are
overall buffed compared to martials
in BG3, sure let's also give martials a buff to help counteract that! I'm not comparing the power of the individual ability that is Sneak Attack to any specific other class ability. And as GWF is a feat implemented in BG3, there's no reason to set it aside. (Even if we did, none of the above premises change. It's still a strict buff for rogues).
Do you disagree with any of the premises above? And if not, do you think that giving rogues the ability to sneak attack with all (including heavy) weapons would make them too strong in BG3 or wouldn't be enough of a buff? You've specifically said that [paraphrased] "allowing sneak attack with any non-heavy weapons wouldn't be much of a buff;" do you still think so if we include heavy weapons, along with GWF and any other heavy-weapon related ability?
