F-16 qualified Ukrainian F-16 pilots are a lot harder to come by and more expensive than the F-16s the Ukrainians are flying.
That's the story but may not be the real story. I would not assume the pilots were Ukrainian.
Senator Lindsey Graham issued a press release last month that he and "Da Nang Dick" Blumenthal supported Zelensky's call for retired NATO F-16 pilots to fly for Ukraine.
https://www.lgraham.senate.gov/public/index.cfm/press-releases?ID=DB12ABDA-0E2C-4CD8-A5C2-D38B10837851
"We will introduce the Stand With Ukraine Act, led by Senator Blumenthal, when the Senate reconvenes in September."
"President Zelensky told us both that he would be looking to supplement his Air Force by establishing a program to enlist retired NATO F-16 fighter pilots. We support this effort. Ukraine is already fielding units of freedom fighters on the ground, and this volunteer force should be replicated in the air."
These make the F-16s a threat to Russia. The Storm Shadows and ATACMS, the Russians can deal with. The JASSMs might push the Russians over the edge.
“The latest development worthy of discussion in last night’s edition of the talk show is the likely fitting of America’s air to ground JASSM missiles on the F-16s that have been and will continue to be delivered to Ukraine.
The acronym of this Lockheed produced weapon stands for Joint Air-to-Surface Standoff Missile and its salient features are its range and its nearly undetectable characteristics in flight. The missile apparently has two basic variants, one for approximately 400 km and the other for 900 km.
The logic for fitting a couple of these missiles on an F-16 is to enable the jet to strike deep into Russia, as far as Moscow and beyond, even if they fly well back from the Russia-controlled territory in Ukraine to be safe from Moscow’s advanced air defense systems.”
Gilbert Doctorow