Or you could buy Ghostblade and get stats that synergize. Ghostblade active gives less AS than a stacked GRB, but GRB wastes so much time and potential costs. At first I was dismayed the YGB had crit removed, but with the changes to Zeal item builds, I'm actually getting much much more slot efficiency with YGB's higher AD and Shiv's higher crit/AS.

The powerspike on YGB is so big because of several things:

The Mv Spd from the active and Highlander stack additively.

It builds entirely out of items which have beneficial offensive stats. Building a Blasting Wand on Yi is the last thing anyone wants to do. This means that you are missing out on small but meaningful powerspikes while you accrue 1925 gold after the pickaxe in the GRB recipe. If you don't also build Hybrid on hit items, you are missing out on a lot of the efficiency of Rageblade. Yi isn't Jax or Xin, his only ratio is 0.15 on Meditate(crap). There might have been a case for this before its cost nerf, but I don't agree with it now, especially with the pen buff for AD assassins. Riot's intention is that assassins will go into cunning for flat pen, burst damage, and %dmg bonuses. With 12-18 you get all of the % dmg bonuses possible. YGB and Maw are both core items on every AD assassin right now.

Stacking flat penetration is the only thing that will let AD Yi burst champions in 2-3 hits other than building full hybrid on hit. Pen stacking AD Yi can three shot squishies at 3 items instead of the 4 it takes for Hybrid Yi.

YGB offers 4/5 of the primary AA stats in large numbers in one item, the only thing lacking being crit. 65 AD, 20 Flat Pen, 40%AS, 20%MS, 10%cdr(not primary, but increases ult frequency). The active is on a 45 second cooldown. It lost crit, but a Zeal as a 3rd item gives 20%, then Shiv or PD gives 30%.