Prepare for some very unpopular opinions here:
Rafael Fiziev has somehow only fought strikers. Extremely padded record, prior to the UFC he fought three fighters with winning records and they all won all of their fights in suspect organisations via 'Punch'. Watching the fights you can see they all try to through hands with Fiziev and don't even try to utilize a kicking game. It's weird. The guy is a Muay Thai coach for Tiger Muay Thai, has been competing in Muay Thai since he was 12, and you're gonna go in there with a rudimentary boxing approach? Yikes
Anyway, first instance with the UFC Fiziev gets put out immediately by a spin kick from Mustafaev. Can't blame him for that too much, Mustafaev had a lot of unknowns, threw the kicks fast with no wind-up and Fiziev is a notoriously slow starter. Maybe he was worried about grappling too, it's tough to say
Against Alex White... He won comfortably, but I can't say he looked good. Alex White is a BJJ guy with no real wrestling background and unspectacular striking. Fiziev outlanded him significantly BUT holy fuck the dude got hit clean A LOT. It's possible he just had no respect for Alex White's power, and fair enough, but you'd still like to see a lot more defence than Fiziev was showing. He also wasn't able to put ol' gasoline head out despite the fact White had been KO'd before (and stunned badly by Jim Miller no less), and despite visibly rocking White on a couple of occasions. In fact he didn't really show any killer instinct in these moments. He was however able to stuff a couple of single legs and naked double legs without ever looking in any real danger of being taken down (his double leg defence on a couple of occasions was a guillotine he used to knee his opponent in the face, which was awesome). There was a couple of occasions where White was holding Fiziev's leg up high and could have had a trip but just... Didn't even attempt it?
Marc Diakiesie is an athletic fighter that is known for his flashy striking style but initially started out as a grappler. He dropped three UFC fights in a row, but that's kind of misleading - Drakkar Klose caught him off guard with calf kicks, Hangman Hooker caught him in a guillotine due to reckless impatience as a result of frustration that they weren't fighting a banger for the fans, and given his slow start/lax nature in the opening rounds of the Haqparast fight it kind of seems like Diakiesie wasn't taking him seriously (the two were also former training partners, which complicates things - see: Khama Worthy v Devonte Smith). One fair criticism of Diakiesie is that he needs space to use his reach and fight his game properly and he struggled with the relentless pressure of Haqparast's boxing approach. Diakiesie's adjusted for this by adding calf kicks to his game, but neither Duffy nor Lando Vannata are pressure strikers so it's possible this is just a weakness that hasn't been properly exposed since
Fiziev doesn't have the footwork of Haqparast, is more hittable from the outside (as Alex White demonstrated), and his general conservation of energy in a fight means he's less likely to bomb forward non-stop to replicate Diakiesie's last loss's success. Diakiesie's grappling prowess and the question marks around Fiziev's defensive grappling offer an alternative path to victory (or a threat which makes the striking game easier), and Diakiesie's addition of calf kicks which I don't believe have been part of the Muay Thai meta creates one more puzzle for Fiziev to solve. Despite this, it's possible that by crowding Diakiesie with strikes and giving back combinations on the counter like Haqparast did in the first and second round respectively, Fiziev could knock Diakiesie down and secure his own path to victory
The current lines seem very fair and although I lean Diakiesie at this stage, the price of 1.58 is far too steep for a play due to Fiziev's power/pressure game/striking nous