I got started playing poker back in 2013 on the FT play money tables. Within the first two months, I made it to the play money nosebleeds with like 10BI for KOTH(king of the hill deep HU), and around 40BI for the highest running 6 max tables before losing it all at KOTH.
My recollection about the level of play there is hazy because I was brand new to poker and because it was a long time ago, but I do remember playing with Berry Johnston (lol), and some other decent US players (and random ft pros) playing there out of boredom.
I recall the atmosphere at the nosebleed play money stakes being at least somewhat serious, and it seemed like most were making a decent effort to play well. This makes sense, since this was before you could officially buy chips from the site and so there was a black market where you could sell play money chips for a pretty penny. (The bulk sale rates had the nosebleeds being like nl25, and KOTH being nl100 IIRC) I should also mention that the games at the time were rakeless.
In retrospect I must have sunrun to even get there that quickly. I remember thinking 6-8BI was enough to sit the next stake up, haha
Could some of the KOTH matches have been at a similar level of quality as a typical nl100 HU match of the time? Sure. But even with black market rates, I'm sure the games ran much softer than their equivalent stakes. I don't know anything about the current play money black market, but I don't see a reason why it would be much more difficult today under normal assumptions.
That being said, I suggest OP put his money where his mouth is and play me at nl100.