OP has a pretty clear agenda here. Of course, though, this can easily be countered by the fact that players don't ever decline (or improve, if you'd like to go that direction) in a completely straight line. Take the following examples:
2010 Wimby Fed: One of his worst Wimbledon tournaments; went five with Falla and got dumped out of the tournament rather too easily.
2011 Wimby Fed: Not a bad tournament from him, though far from his best. The Tsonga match was brutal. -Improved from 2010-
2012 Wimby Fed: Definitely a much better performance than the previous two, after a shaky match with Benneteau. Beat a good Djokovic and a very good Murray in the final rounds. -Improved from 2011-
2013 Wimby Fed: lol. -Declined from 2012-
2014 Wimby Fed: Much better than 2013, though that isn't saying too much. Still not at his best or even as good as in 2012 but he delivered some solid performances and even took Djoker to five. -Improved from 2013-
2015 Wimby Fed: I consider this version of Fed to be even better than in 2014, especially before the final. Other than that, ditto. -Improved from 2014-
2016 Wimby Fed: He struggled a lot here, but that was mostly because of the injury. -Declined from 2015
2017 Wimby Fed: Pretty clean tennis here; didn't drop a set. Probably not as good as 2012 but I'd say it's at least on par with 2015. -Improved from 2016-
2018 Wimby Fed: Nice enough in the early rounds, but his form took a massive turn for the worse in the Anderson match. -Declined from 2017-
2019 Wimby Fed: Despite some iffy opening matches, Fed played pretty well up until the final. Even in the final, he played pretty well except for the big points which really punished him in the end. -Improved from 2018-
This "decline" or "evolution" of Fed's performance at Wimbledon is in no way linear (although, overall, it definitely trends worse). His best showing was pretty clearly 2012 but there were some gaps between his good performances.