With one exceptional club in AS Monaco who could succeed in D1 the average D4 side is as good as the average D3 side.
At least statistically speaking D4 has a better club than anything in D3 and D3 has a worse club than anything in D4. The world has gone mad!.
This should give you the idea that D4 is a wide open mad world where almost anyone who gets promoted could then go on to have a second good season , so probably D4 sides could see a double bounce as a quite reasonable prospect.
Monaco’s big problem is a weak keeper for such a good side. They will prosper in D4 but everyone knows , bye pass the midfield lump the ball up to a big striker. This leaves them vunerable to the likes of Espanyol, Anderlecht, Hellas and Aston Villa all who could challenge them.
Espanyol are the most balanced side and should concede the least goals.
Anderlecht should expect a good finishing position but do they have the depth for a full season push. Their Belgium rivals don’t have that issue but a weak offense is likely to be their achilles heel.
There are a number of relegation possibilities all the way up to Bordeaux should be concerned. Zagreb are strong enough at the back , but where will the goals come from, Stuttgart doing well for now but lack depth and have defensive frailties. Dynamo Moscow more than any team can not afford a single injury without the team suffering.
So finally D3 and D4 seem to have merged ratings rise, at least for now, however some old timers may see their last few season in D4 and the rating drop will come sooner or maybe much further in the season.