I disagree with the notion that Fuglsang has suddenly become a top gt rider, he only has one top 10 finish in a gt and that was in 2013. Yes, he suddenly improved, but in the races that always suited him more, shorter stage races and hard one day races. That said, last year he was the most impressive road cyclist of the spring season. With Lutsenko it is also mainly results in shorter stage races and one day races, but some of his performances are really out of the blue, mainly him dominating 2 editions of the Tour of Oman and also finishing first and second on the MTF and finishing top 10 in the Dauphine and top 20 in the Tour while being a domestique.
I searched for GT and grand tour in this thread and can't find the notion that you disagree with.
And regardless of what races suited him more, an improvement at age 32 after 8 pro seasons is not normal.
By the numbers
top-5 in major shorter stage races
2009-2016 - 3
2017-2019 - 6
best finish in a major short stage race
2009-2016 - 3rd
2017-2019 - 2x1st, 3 times better finish than the best finish previously
1-day races best finish
2009-2016 - 2x4th
2019 alone - 5 results equal or better than 4th
yes, he has an Olympic silver, but some fortune played a part in that unlike his 2019 1-day rides where he was arguably among the very strongest in each 1-day race he did in the spring