Its not that multiclassing is good or bad it is Larian removed the minimum requirements to multiclass. This is what creates balance in 5e... well as balanced as you can get.
And well if you have been DMing for 20 years you should know that "Timmy-the Power Gamer Munchkin" player type. That is pretty much what you see in these forums and on Steam all the time. People spreadsheeting their way to easy wins on mid tier difficulty and then moving on to the next hotness for the achievements or YT/Twitch views.
