I do think he's actively declining, not even standing still.
He's lost the youthful insanity that we all have at some point, but he hasn't replaced it with a mature resolve.
He's naturally very fast, but I don't know a) how badly he wants it, b) how hard he works, or c) how much he invests in sprinting, as far as his life is concerned.
I haven't seen any of his weaknesses improve, all I have seen is his strengths dwindle. Meantime, Vicaut has been exactly the opposite. Vicaut, you know--he trains hard and consistently, and is visible in not only his training but in competition.
Lemaitre? Invisible. He needs a better environment. He needs a different coach. He needs to not be satisfied. He needs to not look UP to those who are ahead of him, he needs to believe that he has arrived, that he has every right to be up there WITH them, and to not be satisfied until he is.
He totally has the equipment, his is a failure not of ability, but of training, motivation, environment. That guy should have already gone mid-9.9x BASIC, a time he hasn't touched.
So much talent, and his time is running out. Now he will be playing catch-up. The result will be either slowness through desperate overtraining, or injury, likely both. He is losing his teenage neurology every day, but isn't replacing it with mature control and power. He hasn't developed into an adult sprinter.
If we don't see anything from him this year, we can conclude that he is finished, for good, unless he goes for "medical treatment".