In defense of JDA, those who have rejected it have done so because they consider it an outlier in three respects. 1) Genos should not be that strong, 2) Elder Centipede should not be so durable 3) the calc is an outlier compared to other dragon level threat calcs. Let me address these points.
1)
Genos should not be that strong when he fights Elder Centipede - Genos has had at least 4 upgrades and possibly as many as 10 (
https://anime.stackexchange.com/questions/51473/how-many-times-was-genos-upgraded) between his EC fight and Beginning of Series and these upgrades are generally featless and only scale to characters who scale off of Genos, so they only upscale vaguely. This ambiguity means that we can reasonably assume Genos is anywhere from 7-A to High 7-C by the time he fights Elder Centipede. If you lowball Genos and say each of the four major upgrades was a 1.5X increase, Genos would still be High 7-C at 858 kilotons. But if you highball Genos and say there were 10 upgrades (based on the manga visuals) and each was x2, he would be 115 megatons or 7-A. Before you say that's an unreasonable highball, is going from High 7-C to 7-B over 4-10 upgrades more of an outlier than going from "at least High 7-C" to High 6-A with Ultra Spiral Incineration Cannon in a single upgrade? Genos has been upgraded so often that there's no concrete narrative nor mathematical reason he can't be strong enough to break a high dragon's tooth at this point.
2)
Elder Centipede is not that strong of a Dragon Level Threat - Elder Centipede is all about durability and survivability and he excels in those two categories. According to Gyoro Gyoro, only 4 S-class heroes could possibly defeat him, all of whom are far superior to ordinary dragon level threats. Even a duo of High Dragons like Bang and Bomb stand no chance against his overwhelming durability + crazy regeneration. As Gyoro Gyoro argues (stick around and S-class heroes will give you broken bones, Gouketsu) and most will agree, other high dragons like Gouketsu and Vaccine Man could be overwhelmed by numerous heroes as strong as Bomb and Bang. There's no reason Elder Centipede isn't in the same ballpark as some of the other more powerful dragons, although it merits this rank by durability and survivability as opposed to speed and power.
3)
this calc is an outlier among dragon level calcs - The lowest dragon level calc I could find was Beefcake's canon height LE, followed by Vaccine Man's explosion. The Beefcake 270 m LE was high 7-C and the Vaccine Man bomb was 7-B. If we want to talk about outliers, I would mention Geryuganshoop, Pluton and the Meteor which have 6-C, 6-C and High 7-A calcs respectively. Other dragon level calcs have LE's in the 7-B range and high ends in the 7-A range very close to JDA. Namely, Gouketsu. His LE cloud feat is 7-B/33 megatons (notably lower than JDA), his ME is 7-B+/94 megatons (10 megatons higher than JDA) and his HE is 7-A+/846 megatons. Similarly, Beefcake's calcs for his depicted height (although his canon height is 270m, he is drawn between 2000-3000m in most shots) give 7-A and 6-C results. Therefore, dragon range calcs range from High 7-C at the very lowest end, to 7-B on most LEs to 7-A and 6-C for many different calcs. Just because our current ratings are 7-B and low 7-B does not mean it is impossible that many higher end dragon level threats could be 7-B+ or even 7-A. Our calculations certainly support the possibility.