They compress the time on "House of the Dragon" which makes sense, so they don't have to cast a child for certain events in Rhaenyra's life, and can simply use the youthful-looking woman to play her as an adolescent. THAT is an example of it being "necessary for casting and a TV show".

On the other hand, the extreme time compression is not necessary for LotR:RoP. We are talking over a millennium. The aging of the actors is just not in it! The characters who might have been contemporaneous with Eregion and with the fall of Numenor, are immortals. You don't to put Elrond and Gil-Galad in old man makeup or need a new actor to play Galadriel (not that it would not be appreciated) in the latter era.

The only way time compression makes sense is if you have a limited number of episodes to cover all the material. Instead, they are seeking to profit by displaying as much footage as possible, to entice people to watch Amazon. So it makes sense that they would want to spread the story over as many episodes or seasons as you can. So do Eregion in one season, culminating in the war against Sauron, with Numenor coming to help. Then in the next season, we can catch up with the descendants of the king who came to the aid of the Elves, and see how it's not going well. Now, if you want to compress stuff into these two incidents, that would be an acceptable necessity. For example, there was, at some point, a princess of Numenor who was the eldest child and should have inherited the crown, but was passed over, and married the lord of Andunie and became the ancestor of Elendil and Isildur. Regardless of where she was in the history, you could have her be part of the generation that fought beside the elves against Sauron, so that when we get to the latter years, that inheritance controversy has blossomed into a split between her descendants who are Faithful, and the descendants of the brother who gained the crown, and have turned against the Elves and the Valar. You can take advantage of the time stretch to accelerate the depiction of the changes, rather than make events happen too fast. As it is, they have left themselves almost no room to tell the story as it exists in the book, where they captured Sauron, brought him to Numenor in chains, only for him to flip the power dynamic and convert the King's Men to the worship of Morgoth, and persuaded the king to invade Valinor. How much footdragging are they going to do in Numenor while keeping Sauron in Middle Earth for his necessary role in the eponymous rings, before he can come to Numenor to lure them to their destruction?

I can't see how messing with the timelines was necessary or anything but an impediment, much less an improvement.