How are today's optics compared to the old iron sights and what is the difference in training with the two?
There is no reason to have irons other than as a backup to your backup reflex collimator. Optics make everything better.
Optics certainly make things easier. A scope or reddot is just putting the dot on target and you got it. scopes also magnify adn ake spotting the target easier. Whereas with iron sights you have to line up three parts: rear sight, front sight and target. You have to teach the prospect rifleman how to properly focus his eyes on front sight and target and not the rear sight. Also to put the face ion the right and repeatable way on the rifle. A reddot is much more forgiving, scopes depend on the model though general issue scopes normally are built to be used with not optimal hold in mind.