Sunlight is the new and very serious challenge that Morgoth's armies are facing.
We proved in Season 2 that an army of trolls could very much take on an army of Noldor and win soundly. Morgoth thought he'd won the arms race. And now...his crack fighters *turn to stone* when the Sun rises each day. That's...quite a set back!
The first solution is not to alter the orcs or trolls, but to try to block out the Sun. Let them fight under cloud cover. Or, rather, volcanic ash clouds. Something dense enough to blot out the Sun temporarily, but long enough for him to move armies over the course of days or weeks.
But it can't be comfortable fielding an army when a strong wind will defeat your plan utterly.
So, yes, the next stage is to beef up the troops, make them resistant to sunlight. There is *no* progress with the trolls. They turn to stone, full stop. That leaves the orcs. The orcs are
afraid of the Sun. They cower and hide from it, filled with dismay. Something can be done about that, in the 'I'll give you something to be afraid of' manner that we would expect from Boldog and his ilk. This might be the first time we see orcs driven by lashes to move in daylight. But they could still try to arrange to fight at night, at least.
I was going to point out that Angband is very far north, and thus has long nights in the winter and short nights in the summer, but...this is pre-round world, so never mind
So, between trying to figure out how to get his troops dealing with being outside under Sunlight and Moonlight, and replenishing the numbers of his vastly reduced armies....the fact that an army is fielded at all at Dagor Aglareb is an accomplishment.
Angband should always have cutting edge military technology. Morgoth doesn't lose because his armor or weapons are inferior.