In my opinion, I don't believe Runaan's is worth building. My build consists of rushing IE into boots then PD.
Afterwards I choose to build LW or BT/BOTRK depending on their comp. If they've build some armor, I go LW. If they haven't I build BT unless they have a lot of champions who stack health or if I need the kiting power of BOTRK, such as if they have Maokai and another high health champion like Vlad. I rarely build BOTRK though.
Then I build whichever item i didnt build in the last step. I then finish with my defensive item, which usually ends up being Scimitar for the debuff removal.
Ill sometimes switch up my build by selling my doran's blade for vampiric scepter if it's later and I just need a slight boost to my lifesteal. Or i'll build QSS and finish Scimitar later if I need the debuff removal.
Based on what you have said, it looks like you miss out on your either your boots or your defensive item. Boots are basically essential. Sometimes I'll sell them late game and buy zephyr, but usually the game ends before that and having homeguards is more useful.
If you miss out on your defensive, that can work. But I find that going full glass cannon ends up being risky because the enemy usually has at least one person who will dive on top of you and do everything they can to kill you. This is why I'll almost never build Runaan's on Jinx. I find her too vulnerable to forgo the defensive item. Even a Scimitar helps because of the MR and removal, even though it gives a good amount of AD.
Runaan's being a replacement for PD....I don't think that's a good idea. I just find the stats of PD to be much more useful. The Crit chance increases your damage output by a very large amount. The attack speed is good enough to make a difference, but it doesn't give too much to max your attack speed in mini gun form and it allows you to stack more AD. The passive lets you avoid body blocking as well. You don't really need to wave clear because the AOE from Jinx's q is very good already. Runaan's only really helps in a teamfight if the enemy is grouped together. If enemy shouldn't really be making that mistake in the first place, and extra AOE Crits that PD will give you can still be useful even in that situation. Runaan's doesnt give much in 1v1 situations as well.
