That's not what the article says.
The article uses the past tense. As you quoted...
"Sources have told Deadline that Netflix have been proponents of a 17-day window which would steamroll the theatrical business, while circuits such as AMC believe the line needs to be held around 45 days."
Note that it doesn't say "are still proponents...".
However, the article also says Sarandos says...
“There’s been a lot of talk about theatrical distribution, so we want to set the record straight: we are 100% committed to releasing Warner Bros. films in theaters with industry-standard windows.”
It's clear that Netflix once eschewed theatrical releases. But they kept dipping their toe in it. And in order to assuage anti-merger proponents, they are saying (whether one believes them or not) that they will adhere to the industry standard, which is significantly more than 17 days.