Nothing you quoted invalidates my point. PHB doesn't say it's not flammable, it has historically been flammable, and people don't follow/agree with Sage Advice. Simple as that. It's not a BG3/PHB difference, it's a BG3/Sage Advice difference.
Plus, if we followed the Sage Advice reasoning, there are a TON of things players and DMs pull that are "against the rules" because he's taking a 'only things clearly defined are allowed' stance in this instance when it's not taken in any other instance. Can a player recover caltrops? The PHB doesn't say they're "recoverable" so the Sage Advice logic says no but a practical application would be that of course a player could spend 5-10 minutes picking them up.
I changed my text to leave Grease more open ended. I'm going to test the spell soon, as it might just be that much more of a utility thing being flammable. Either way, this list of differences isn't to poo poo devs or to champion Rules Lawyers...it's just to give people a guide to things that might not be what they expect, and if something really sucks, we'll be honest about it.
I really appreciate you speaking up about Grease though, I've never seen anyone use it in a P&P game as flammable, but that doesn't mean that it wouldn't be a better spell for it.
"Old time love song will die so swiftly. You never trust me- For a while it was nice, but it's time to say bye....
I'm cold, you're so cold- You're so cold, you're so cold- No-no-no, cold, you're so cold...."