That's what's so frustrating about this show - so much money getting thrown at a show whose story obviously wasn't worth it, whether that's the writers' fault or more high-level executives taking a bunch of bad decisions. But unlike you I see it as a bad script ruining a show that did look great and had solid to good acting - amazing visuals and good or even great acting can't save a show if the script sucks, but that doesn't mean that the visuals or the acting themselves also automatically suck.

As you say, the cast salaries should be on the modest side here considering the lack of big names. But they definitely didn't hold back on using a wide variety of sets, all of which looked great in my opinion, not only Numenor but also the Lindon and Hollin ones, the Moria ones, the 'Southlands', the sea, etc. In some cases, like the Valinor scenes, they went to a ton of effort and expense for just a few minutes of actual screentime. Just because what happened there was often stupid doesn't mean it didn't look good. And while the number of people involved in the battle scenes on screen was tiny compared to the scenes with thousands of combatants we regularly saw in LotR, the latter obviously used CGI to a considerable extent to pad those numbers - I don't know if they actually needed so much fewer extras here. On the CGI/Visual Effects side, I won't claim to be an expert judge but I do see comments that they're very high quality - and no doubt cost a fortune.

For comparison, the cost of this show on a per episode basis (and excluding the 250 million USD they paid for the rights alone) is 58 million USD - which is a staggering number, but Stranger Things Season 4 is at 30 million USD per episode and while they obviously need as much or more CGI/VFX, I don't think they have nearly as many fancy sets they needed to build. Especially considering theirs is a fourth season and many sets were already built in the earlier seasons - estimates are that RoP's next four seasons, if realized, may cost only a bit more combined than the first season did alone, which suggests their cost per episode would then drop below Stranger Things'.

Back at the time of the original LotR trilogy twenty years ago, their budget of around 300 million USD was considered humongous - while a contemporary genre TV show like Buffy the Vampire Slayer had a budget of about 1 million per episode, increased to 2 million later on. Nowadays, the likes of LotR would likely cost, what, triple that number?, but for the TV shows we're talking 15 or 30 times the cost. For the simple reason that Stranger Things or RoP are made to movie standards, with no longer any significant difference in quality or creative constraints between movie and TV, so also no significant difference in their respective costs per hour of content produced.