been a while since I've played 8, remember the junction mechanic pretty much being the most important thing to making a strong team other than the card ability that let you get items out of them.
been a while since I've played one in general actually, last one I remember was 12 that I rented a few years back.
and yeah, nippon ichi's niche is basically games with pretty deep technical mechanics that can be ignored for the main story but are extremely crucial to late game success, especially so for getting maxed out characters.
phantom brave was throwing the failure title on a weapon, ideally something with lots of speed, combining items, then moving the failure title back off the weapon for a good title. (failure was -80% to stats, so it made improvement pretty easy for a while.) basically made marona a one girl army that could kill everything before anything but her got a turn in. XD
makai kingdom was just heavy focus on reincarnation basically, reincarnating characters many times over into starred items made them really strong. Items were sort of secondary in that they can't be improved upon too heavily.
then disgaea is the opposite of makai kingdom thanks to item world, a random dungeon that levels your items which increases said item's stats. An example of this in disgaea 4 just to show how broken it can be: a fresh trap(best emblem in the game) gives ~7000 to all the basic stats, a bit more to hp and sp. A level 300 one gives ~510,000 to all stats, taken even further, a level 300 one that has had the item god(final floor boss) killed ~67 times for the bonus gives a solid 2.1 mil to all stats.