I've had the same problem as everyone else, I've started again around 3 and each time the same, a good run for around 10-15 games, followed by heavy losses and eventual sack. I tried other tactics posted on Forum's but they don't seem to correspond to success on the Switch.
Somehow, this week I started again (again, again, again) with Fortuna Dusseldorf and clinched promotion in the first season.
Tactics (off the top of my head as I'm at work):
3-5-2 (modified):
Will show it as a 5-1-2-2, using 3 CB's (1 BPD), 2 WB's, 1 BWM (sat in DM), 1 BWM (sat in CM), 1 DLP (sat in CM), 2 up top (AF, Trequartista).
Other tactics were playing through the middle and play from back with mixed passing, run at defence, with a Control/Structured setting.
Inevitably I hit a poor run of form, at which point I moved my DLP into AM which brought it back round, when I hit another couple of losses I hit back.
In game management if I was struggling I switched to direct passing and early crosses.
Strikers hits a combined 40 goals.
Will let you know how I get on in the top tier (surely back to consistently bad).
Cheer