Mate, there's no such thing as "second season syndrome" and your results easily might be worse in the next season than your results in the current season even if your team is improved in the next season.
The weaker your team and the more challenging your competition, the more random your results will be.
Let's say there are 20 teams in the league and you manage a team that is predicted 15th and if you use a good tactic that allows you overarching above your media prediction then I'd say you might finish the season in this range from 1st place to 10th place and these factors will have impact on your result:
1) The difficult level of the competition. The higher reputation a completion has, the more challenging to play and overachieve in it.
2) Luck.
If you play with a weak team that has about 15th media prediction in any low reputation leagues then with some
average luck you probably will finish the 1st place or at least in top 2 but if you play with a weak team that has about 15th media prediction in any high reputation leagues such LIGA BBVA or English Premier League then probably with some
average luck you'll finish only in top 5 and that's how the game works.
Imagine, that you were playing in some high reputation league and were extremely lucky and that allowed you to finish the 2nd place with your team that had 15th media prediction so after that many FM players start to think if they slightly improve their teams in the next season then they just must win the league or at least easily finish the 2nd place again and when it doesn't happen then it causes great frustration but their false expectation is the root of all evil.
Usually, if you played in the most challenging leagues such LIGA BBVA or English Premier League with a weak team that had media prediction about 15th and you used a very good tactic and had some luck that allowed you to finish the 2nd place then the best what you can do is strengthen your team to have media prediction about 10th in the next season and this mean that your range for the next season will be about from the 1st to the 5th place and if in the next season you finish the 5th place then it's still a very good result for your team that were predicted to finish 10th but many FM players get frustrated when they finish 5th place after they finished the 2nd place in the previous season because they don't understand how the game works and it really doesn't matter what place you finished in the previous season and the only what matter is your media prediction in the current season and your place in the current season compare to your media prediction...
Mate, I suggest that you'll take all what I wrote above into consideration when you evaluate your results and make any conclusions.
In summary:
When you evaluate your result you should look at 3 things:
1) The reputation of the competition you play.
2) Your media prediction in the current season.
3) Your result in the current season.
The most common mistake that many FM players make is that they look at their place in the previous season when they evaluate their result in the current season.
Also many FM players wrongly think that if they were able to win some low reputation league with the weakest team in that league then should have the similar success using the same tactic in any high reputation league but that's a very wrong thinking because the difficulty level in the low reputation league drastically differs from the difficulty level in the high reputation league and AI mangers in the low reputation league are so poor that they use poor tactics and they aren't able to exploit weaknesses in your tactic.