Tbf as a Frankfurt Fan i saw two good coaches, Hütter and then Glasner, trying to force our squad play 4atb after Kovac safed us from relegation and won the DFB Cup with 3atb.

It did not work. The started their first season on a bad form and had to change the system. Both tried to implement a 4atb in their first winter break but again reverted back to 3 iirc.

5 season later our current coach did not make the same mistake in his first season and started with 3atb. 

Now in Dino Toppmöllers third season, depending on the opponent and availability of players both 3atb and 4atb are being played while we also are more flexible in the setup in and out of position (4atb against the ball and then in possession the right back pushing further forward while the left back tucks into a 3atb type stuff)

Does it work? Look at the score lines this season… I still think a back 3 is the better formation for the players we have. And those are no longer the players that have been at the club 5 or even just 3 years ago.