Except when playing Nadal on clay, I felt like he was too passive between 2012-2014. That worked to win smaller tournaments, stay #1 and get him into Slam finals. But he ended up in a lot of close matches in Slam finals/semis against the best players like Federer, Nadal, Murray, Wawrinka due to not being more aggressive and lost several of those matches in that period. His serve was also not as reliable to get him out of trouble under pressure and I don’t think he had the mental belief that he was better than Federer, Nadal, Murray yet.
I think in 2015-16, Becker had improved his serve, he started hitting with more topspin which reduced his errors while playing offensively hitting the ball more on the rise and he started playing more aggressively. This resulted in a couple of unbelievable years where he started believing no one could touch him when he played well and after his slump in 2H2016-1H2018, he seems to have retained that confidence. I think that confidence can be shaken only by Nadal on clay.
Compared to 2015, his FH is faster/bigger but with less spin, his BH is prone to more errors, his movement is not as good, his serve is better/more precise/bigger on big points, his return is as good, his net game is better and his variety/slice is better. So, what he has lost in movement, BH reliability and FH spin has been compensated in other areas. Physically, I think his speed and change of direction is slightly worse than his peak, but his endurance is still there and he knows how to manage his mental (wolf?) energy better in a long match to peak at the end. He also plans strategy better for different opponents using video analysis/stats while he used to play somewhat the same way in all his matches in the past - I think that is an improvement on tour for all the top players whose coaches study videos and stats of opponents more. He also now has the aura of being a 22-Slam GOAT contender along with long winning streaks at the AO/FO which makes it tougher for opponents to have the belief they can beat him at Slams.
So, is he better than in 2015-16? If you look only at his baseline game, I would say not as he was at a BOAT level in those days. But, is he as tough to beat? The answer to that question might be that he is almost as tough to beat as at his peak because of all the mental/confidence/strategy gains in addition to better serves, more variety, bigger FH when needed and more confident net finishes. A better serve under pressure can make up for a lot of decline in other areas as tennis is a very serve/return oriented sport.
