I think your arguments are way too weak on this. Luck is a terrible argument because people can say that about wildcard too and everything else. The 20 kills badge requires luck just like everything else but it also requires skills, people need to understand how to traverse the maps efficiency to increase their chances to get the badge. They also need to be so good at the game to the point they can usually 1v3 and understand how to survive extremely well that they rarely lose. The 20 kill badge is usually only for the top 10% of players and was a big goal for people who cared enough about the game to go after it. Cheaters is also a terrible argument for the value of a badge because people can say that about everything else too.
The raw truth is that people that couldn't get the 20 kill badge in the BR usually ain't good enough. There's reasons why players with a 3 K/D or higher can consistently get a 20 kill game in the BR without complaining about luck. It's because they are skilled enough and experienced enough to get it.
Getting the badge in wildcard is so different to the point it there should be a different 20 kill & 4K damage badge for that game mode. In wildcard people don't even have to learn the bigger maps, it's basically just a TDM mode that allows average players to get the badges because they can pretty much die as many times as they want. A 1.0 K/D player can eventually get the 20 Kills and 4K damage badge through wildcard.
Now the badge is already ruined it doesn't mean anything anymore, just like the master badges. There's gold and plat level players with masters badge because of how terrible some ranked seasons were.