The pro scene was pretty healthy till 2018 at which point owl started EU suffered from a lack of funding and tournaments in 2017 leading to a lot of their individual players being poached. The one "EU" based team in owl signed Koreans because they were c9 and they had a Korean team pre owl. Teams realised that most of the most cracked players were Korean so either built full Korean teams or mixed teams. The year before Valo release ow had suffered a year and a bit of a meta called GOATs which had no DPS so dps players were on tank. Most notable names to transition have been mentioned but Babybay, Sayaplayer, Corey, Rawkus and Sinatraa were the most notable in OWL with the latter being the previous years MVP.
Outside of OWL enghh, juv3nile, Klaus, patiphan, em1l, boostio and Derrek. Currently a lot of KR owl players play Valo in their free time most notably a player named xzi made it to rank 1 in kr.
Other things to transition from OW enigma and this website and a lot of the early journalists on it.