Everyone would agree that the Rafale and F/A-18A Hornet belongs in the medium fighter category.
It is worth noting the F-16 Block 60 actually has more engine thrust (32,500lb) than the original F/A-18C (16,000lb x2). The F-16 Block 60 also has a heavy empty weight (22,000lb) than the Rafale C (21,720lb). The Rafale is less than a foot longer than the F-16. I think the F-16 qualifies as a medium weight 4th gen fighter based on the international competition. The bars in the image are for the old F-16 Block 30.
Also in regards to the F-15 numbers on the graph that is clearly for the lightest F-15 model. If we look at the newer heavier variants with conformals they have a heavier empty weight than the J-20 and the original Su-27.
The Gripen, Tejas, F-20, F-5 and F/A-50 would be in the light fighter category.
There is no real logic to the labels besides a carryover from the WW2 standard of heavy fighters being twin engines, laid out like a light bomber, and light fighters being laid out like...fighters. It stopped mattering sometime during the war with aircraft like the Me-262. If Britain were to use the Hawk as a multirole like the Alpha Jet, or buy the F/A-50 or something, then the Eurofighter would go from a light to a heavy fighter the same day. The heavy counterpart to Eurofighter is the Tornado, as evidenced by Germany and previously the RAF, of course.
Equally true it's also possible to describe the Typhoon as the "heavy" counterpart to the JSF, or the RAF as an all-heavy air force since the JSF is actually an attacker like the A-7 Corsair, which in the RAF's case would be closer to true. All of these are true simultaneously. It's like how a Necker cube can be simultaneously viewed from the top and the bottom.
There's no actual weight or whatever where a plane suddenly tips over to being "heavy". This is exactly how the USN got the F/A-18E/F. It's the same question as "what is a cruiser and what is a destroyer". The answer is "it depends on what you need to do with the budget". Which is, incidentally, how the MiG-29 happened when Mikoyan convinced the Soviet government they "needed" a "light fighter" for PFI...
Suffice to say, the distinction is irrelevant. The PLAAF could operate nothing but F7F Tigercats and F-4 Phantoms and it would still be an "all heavy fighter" air force. Just bad heavy fighters. There's a reason the PLANAF and PLAAF are interested in the J-35 and it's not because the J-11 is so good they just need to balance it out. People just like "heavy fighter" I guess because they think airplane classes are like boxing weight classes and there's some hard limit where being 70,000 lbs MTOW vs 50,000 lbs MTOW actually matters.
"Cruiserweight" is a better name for a "medium fighter" because it very deliberately pokes fun at the idea of typologizing fighters by weight instead of...actual capabilities. Even the, now nebulous and poorly defined, "generations" of aircraft that was invented by the Soviet PVO was better for rapidly sorting threats.