EM - Always a good question as to what one actually means by "legacy" or "4gen" or "advanced 4gen". Let's not forget the 2008 paper which compared the F-35 to the Su-30MKI and Gripen C... which pre-date the F-35, in IOC terms, by almost 20 years. If the threat is an even earlier Su standard, or a MiG-29, you can probably score pretty well.