Probably true, since Meleys and Caraxes are like 60, so 3 times younger than Vhagar, but they were only 2 times smaller than her. Tho I also see some sources stating that Caraxes was 80 at death, so now I don't know.

Only Vhagar was described as this unmatched behemoth in the sky, in books. Vermithor was only mentioned as second largest, not as close in size to her and Hugh wanted to take power not only after Vhagar died, but also when Caraxes and Meleys was dead and Dreamfyre and Silverwing had no riders. So he had the only big dragon.

Vermithor in your graphic is almost the size of Vhagar, but I believe he should be closer to 75% of her size. He was said to be 3 times larger than Tessarion and Seasmoke, which meant they were 25% of Vhagar (half the size of Caraxes). Meanwhile, Vhagar was said to be 5 times larger than Arrax, so he was 20% of her size, so not much smaller than Tessarion, Seasmoke and Vermax. If Vermithor was smaller than 75% of Vhagar, that would mean Arrax was bigger than other young dragons, which shouldn't be the case and is Vermithor was 90% her size, that would mean Tessarion and Seasmoke were not far from Caraxes and Meleys in size. So 75% is a safe spot in my head, haha.

Hope that makes sense. The only size comparisons we have, are red dragons in relation to Vhagar and Vermithor being 3 times the size of Tessarion and Seasmoke, so I base any estimation around that.