I agree, 2015-2019 was peak BTG.
BTG started out around 2013ish making regular 5-reel slots such as Gold.
Megaways started in 2015 with stuff like Queen of Riches, Star Quest and Dragonborn. Then of course was Bonanza in 2016 which put BTG on the map. After that was a mix of MW and non-MW like Danger High Voltage and White Rabbit in 2017, Extra Chilli and Donuts in 2018, then Holy Diver and L’il Devil in 2019.
There were a few duds amongst that early era such as Book of Gods but I felt it properly fizzled out after 2019. The only recent(ish) one I can name and really like is Millionaire Rush. Golden Catch was a good effort on the reel-’em-in genre though and they didn’t water it down with copies of copies like Pragmatic did with Big Bass.