As the calculation for Saint-level characters is accepted -HERE.
Now it's time for MC's AP in the same Key to be calculated. It's a simple one as this one will just be a multiplier by x10.
It's stated and has no contradictory feats.
It's also one Book difference between them - meaning the character had time to develop more powerful (12 years).
Has the foundation that one character named Oliver (he appears in a quote in the other blog) who was at their level (Haydson and Linley) but defeated, later one-shot + killing Haydson who scaled to 7-B (the above blog).
Stated by Bebe that Linley is more than 10x greater. Oliver who one-shot Haydson is not even worth mentioning.
“Boss, what are you being modest for?” Bebe said unhappily. “Haydson’s defense was on par with yours in the past. But now? Just by relying on your post-Saint transformation, the defensive power of your draconic scales alone is on a higher level than the combined power of your draconic scales and Pulseguard Defense of twelve years ago. And now, your Pulseguard Defense is more than ten times greater than before. In front of you, that Olivier isn’t worth a fart. Even people on the second tier, like Osenno, don’t dare to offend you. I think…only the five Prime Saints are able to compete with you now.”
Stated to be 10x times more powerful.
''"He had reached the Saint-level in human form. Once he Dragonformed, his draconic scales were ten times as powerful as they had been in the past. His strength and battle-qi had also risen to terrifying levels. Linley could fully understand…the reason why his ancestors, despite not having a high level of insight, could rely on Dragonform alone to defeat peak-stage Saint-level magical beasts."
His strength and battle-qi are 10x times greater.
“A Six-Winged Fallen Angel wants to fight with me in close quarters combat?” Linley’s dark golden eyes flashed with a hint of cold light. Linley was now a peak Dragonblood Warrior Saint. In physical strength and battle-qi alone, he was ten times stronger than ordinary Saints!''
Another thing to take as a point is that those quotes are not even from his peak-point in the Saint-realm, around 50 chapters before it. From those quotes point in time, his strength increased but as he fought with stronger enemies without big environmental destruction. As it can be seen in the first quote its says that only the Five Prime Saints can compete with him but that was before the Necropolis of Gods Arc (last arc for Saint Key) in which his strength reached a point where he can one-shot a Flame Tyrant which a combined attack of 3 Prime Saints was ineffective. He even fought with one million of Saint-level Abyss Demons alone and making short work of them. He also became a Saint-level Magus thanks to his comprehension of the Wind Law - Concept of Velocity. Thus it's not contradictory to say he got at least 10x time stronger. Normally, he should be higher but I don't have feats that can be truly calculated excluding the above ones.
3.2285637e+17 * 10 = 3.2285637e+18 - 7-A (Mountain level)
From the above points, I think his key tier should be 7-A, likely Higher.