WARNING: The following contains major spoilers for The Seven Deadly Sins: Dragon's Judgment Part 2, now streaming on Netflix.
The Seven Deadly Sins is far from a perfect series, and its most overwhelmingly powerful character's underwhelming death stands out as one of its greatest sins (no pun intended). Escanor's demise was a long time coming thanks to the overwhelming power of Sunshine, but the series really drags it out to the point that it loses most of its impact. As the only member of the Seven Deadly Sins to lose their life during the series, Escanor deserved a better death than he got, if nothing else.
Escanor's death had been foreshadowed for a long time, as the Grace of Archangel Mael is too powerful for a human to wield without dire consequences. As the spawn of Indura, a giant monster unleashed by the Demon King, attacks Gilthunder and other Holy Knights, Sunshine-less Escanor steps in, determined to be of use in the fight. Ultimately, he summons Mael and requests to be granted the power of Sunshine once more, knowing that doing so will kill him and likely not be enough to defeat the Demon King anyway.
When Escanor makes his triumphant return to the battlefield to aid the other Sins in their fight against the Demon King, the series pivots to a prolonged flashback of when he first joined the Sins. The best look into Escanor's past the series has ever given, the reason for Escanor's drive to sacrifice himself for his fellow Sins is clear: joining the Sins changed his life when he was just a frightened man with a power he couldn't control and who felt like he didn't belong anywhere. Escanor credits Meliodas for helping him control his power, and the rest of the Sins for giving him a place to belong.
Despite the beautifully executed character arc for Escanor up to this point, when the flashback ends it all falls apart. To gain more power, Escanor converts his own life force into power so that can unleash a new form, The One: Ultimate. Escanor takes on a fiery new appearance that allows him to wield the full power of Sunshine for as long as he needs, but it will certainly kill him. Unfortunately, the nobility of his decision is overshadowed by this form's lack of impact on the battle and the fact that Escanor stays in this state for several more episodes.
The whole reason Escanor was doomed to die is that the power of Sunshine is too powerful for a human body. Yet somehow, when he brings its power to its maximum, he shows no ill effects or even minor discomfort. After so much buildup to Escanor's sacrifice, he doesn't die until after the battle ends much later, and even then his death is drawn out as he calmly speaks to everyone, one at a time. The series spent so much time on the burden of Sunshine and the weight of Escanor's sacrifice, only to let them both fall by the wayside.
Escanor's demise is a low point for the series, as a tragic loss for the Seven Deadly Sins and for how poorly it was handled. He's the most powerful member of the Sins, one of the most powerful characters in general, and he goes out with a whisper instead of a bang. Escanor's explosive power was the cause of his death, but one would never know it with how tranquil his death was. Escanor's absence is felt in the following episodes, but his lackluster death scene, unfortunately, makes even the mourning less impactful.