F35C is not a Super Hornet replacement - that will be the F/A -XXX. The F35C is only replacing the F-18A/B Classic.
The additional Super Hornets are being bought to replace F-18A/Bs which are wearing out as the F-35C slips into the distance. The new Super Hornets will remain in service for many years, every Sqn which transitions to the F-18E/F/G is one that will not transition to the F-35C which will be bought in lower numbers to fit within the remaining cash pile.
As the Sec Def fo Defense stated, there will be no additional funding.