What those articles report is:
1. The CW requested - and got - CPM increases, which is the rate that they charge per 1000 viewers. That is not the ad buy rate, which is (mostly) based on that rate and the number of viewers.
Because the number of viewers keeps slipping, the CW ad buy rates have also slipped. Flash did get a slight increase in the 2017 season because of that CPM increase - not because of ratings/viewers. It lost that increase for the 2018 season. Here are the rates for a 30 second ad, as reported by AdAge:
2015 - 2016 $70,687
2016 - 2017 $60,660
2017 - 2018 $62,425
2018 - 2019 $45,965
Since the CW has to split ad revenue with its affiliates, the actual ad revenue is considerably less.
In 2018-2019, its Tuesday night competitors, who for the most part don't have to split ad revenue, charged:
$201,065 (ABC, The Connors)
$115,656 (ABC, The Kids Are All Right)
$135,960 (CBS, NCIS)
$193,410 (NBC, The Voice)
$111,898 (Fox, The Gifted)
The Gifted, of course, was just cancelled.
2. The second article states that the CW was able to increase its ad volume after expanding to six nights of television.
I'm not saying that the crossovers don't make good business sense for the CW and WB. If they didn't, we wouldn't be having Crisis. But I don't think this isn't about ad rates - the domestic ad revenue WB gets for Flash doesn't even cover production costs.
(See, also, why the CW was able to negotiate a separate rate sheet for its actors, allowing them to pay regular cast members as little as $4000 an episode, and why CW actors keep leaving anonymous comments on Variety articles complaining about their pay rate.)