/NIN is typically used less for DD reasons, and more for damage mitigation. It's only a damage boost if you're dual wielding, which isn't typically the preferred WAR config these days (it was for a long time, and thus may have been last your friend played).
Utsusemi is reliable in its function, and works against magic, whereas Seigan/TE can be better or worse, and only works against physical attacks (plus you won't get access to it until 70WAR/35SAM).
For the more common Great Axe setups, /SAM is preferable due to actually increasing damage output, plus you still get some damage mitigation. That's not to say you'll always use it, but that from a DD perspective, it's typically better.
Ideally you'll have /NIN, /SAM, /DNC (for soloing) and possibly more subs available to you. Honestly, I would stick with /NIN until 70+ anyway, unless you're very confident in your party's support. Ichi->Ichi may not be great, but it's a lot more than one Third Eye anticipate.
Far as TP/WS, that can vary somewhat on your level/activity. Things are rather different at level 90 due to gear selection, mobs targeted, and in the case of Abyssea, massive buffs available.
TP set is geared towards gaining TP, and ideally, doing decent damage per hit at the same time. ACC is a key stat for a while (mostly moot at 90 right now). Haste is great, though you have little available yet - this becomes a much greater focus at high level, and so becomes a key difference between TP and WS sets. Another thing that you'll eventually focus on will be Store TP (for Great Axe) - you'll see people refer to a 6-hit or 5-hit build. Knocking attack rounds off of getting 100% TP means a big jump in overall damage dealt. Lack of gear/trait availability until later make this not really viable for you yet.
ATT is a good thing to have as well, but often is secondary to other things. High level WARs right now are also putting Double Attack items in due to not really needing ACC. That's not something to emulate until you're also higher level.
WS sets depend on the WS in question. As a general statement, you put in a WS set what helps the WS you're using. Haste, for example, doesn't help WS, so for high level, you'd swap out your Haste items for something that would boost WS damage.
____________________________•• Isiolia - Mithra - Pandemo... Asura FU SE ••
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