Just looking at the Welterweight landscape in MMA. This is the best division in MMA, sans Middleweight. It is also the only UFC division, that they don't have a true Champion in.
The lack of a true Champion started when GSP vacated his belt. Typically a tournament would be held, but instead UFC decided a random fight between Robbie Lawler and Johny Hendricks would determine a Champion.
GSP no longer has any claim to the belt whatsoever, he has been inactive for too long, therefore he's irrelevant to this discussion and that adds further irrelevance to the UFC belt that was born from GSP's absence.
Shields has recent and relevant wins over "#3" Demian Maia and UFC Champion Tyron Woodley. Not to mention wins in the past over Lawler and Condit.
Shields wins over Maia and Woodley are basically as recent as Khabib Nurmagomedov's entire body of work in the UFC.
Askren was #5 in the world when he was Bellator Champion. Sure his competition has slipped a bit, but his record is in tact and those guys he fought looked like they had extra help.
Eddie Alvarez being current UFC LW champ really validates Askren's body of work. Then you consider Cormier was from Strikeforce, Conor McGreGOAT came from a relatively obscure Cage Warriors promotion, Woodley himself was a Strikeforce fighter as well. So the idea that the very best have to born and bred in the UFC is not necessarily true. Vitaly Minakov lurks unbeaten at 24-0.
The winner of Shields vs. Askren will determine a true current #1 Welterweight in the world. This will bother some people, because have all grown accustom to the UFC having all the true Champs in every division.
This will be something new. It's pretty exciting.
Deal with it.
They sparred years ago and it was evident they were the top guys besides GSP at the time.
It's a shame that Jake showed Askren all of his tricks, watch for the guillotine. This fight will come down to who wrestles better on the night.
The grappling exchanges and scrambles could be some of the best ever. The IQ wrestling, the catch. The actual best in the world @ 170 lbs.
Who do you guys think would win?
Shields.But I also like Askren's funk rolling.
I honestly think Shields and Maia are the only two fighters that are bad matchups for Askren. 
Maia was not at the level he is at today, when he fought Shields. 