It is okay for
Tolkien to say that he wrote
middle-earth as an alternative history. Because as you already said, Tolkien also said that it cannot be included in anthropological history. There are only 2 main reasons why people think that the
first age is stronger and more mighty.
1-middle-earth contains a theme of decline. Beings and their power fade and dwindle over time.
2-In the first age, there are beings that are not in
the third age. Or rather, in the third age there are only 2 beings that are not used in war.
balrogs and
dragons.
On the first thought, I don't think that the decline of the theme is about the
races themselves and their power. Because wikipedia says that the fall of the middle-earth theme is about
events, only about the devastating consequences of events.
Second thought, the fact that they did not fight in the
War of the Ring, as balrogs and dragons are
Morgoth's most powerful servants, is another factor that brings the first age to the fore. But there are actually some points that are overlooked. The first is that the number of balrogs was only 7. So the number of balrogs was limited, like the
Nazgul had 9. According to the late writings, there were only 7 balrogs. As for the dragons, I think
Sauron didn't need dragons in the War of the Ring. Because according to the tolkiengateway site, the
fellbeasts, which are as numerous as the first age dragons and used as mounts by the Nazgul, are descended from the cold dragons of the first age. The only thing missing is that they can't breathe fire. But the thing is, I honestly think Sauron's infantry forces are stronger than Morgoth's infantry. Because
Saruman's uruk-hais are sauron's
uruks and olog-hais are an upgrade to the first era
orcs and
trolls. They are both stronger and more technical. The other beings are werewolves and the
wargs were the same in the first age and the third age anyway. I think the only thing missing from the war of the ring is the absence of balrogs and dragons, I think is
nazguls, fellbeasts and mumakils closing their absence. Although the nazguls are not as devastating as the balrogs and the fellbeasts are not as devastating as the dragons, they have their own unique power. And this is a very serious problem for
men and
elves in the war of the ring.