It's worth noting that the Sith ISD (Imperial Star Destroyer) seen in "Star Wars: The Rise of Skywalker" was an advanced model known as the Xyston-class Star Destroyer, equipped with a planet-killing cannon known as the "Kyber weapon." This weapon required a vast amount of power to function, which is why the ship had to be so heavily armed. In comparison, the Death Star relied on a single reactor core to power its planet-destroying superlaser, which was also its primary vulnerability.
It's unclear why Ben Solo (also known as Kylo Ren) chose the TIE whisperer over other ships inside the ruins of the Death Star. One possible explanation could be that the TIE whisperer was the only ship that was still operational or had the necessary components to be repaired quickly. It's also possible that Ben Solo had a personal attachment to that particular ship, which was previously owned by his grandfather, Anakin Skywalker (also known as Darth Vader).