Blade weaving: Damaging an enemy champion with a spell increases your Basic Attack Damage (auto-attack damage before bonus AD) by 1%, stacking up to 3 times (max 3% damage increase)

spell weaving: Damaging an enemy champion with an auto-attack increases your spell damage by 1%, stacking up to 3 times (max 3% damage increase)

Ask yourself how many damaging abilities do they have? Think about the uptime on 3 percent dmg increase. So sivir has 2 damaging abilities.

You can keep these up a lot easier as sivir than you could as Vayne for instance. Now, ignoring the builds for a minute, just think about what it takes for you to get to full stacks of blade weaving. You have to hit 3 abilities. So sivir's w probably can proc those, so lets assume you were at full stacks of spell weaving before you throw your boomerang blade. That's going to be a 3 percent increase on your q's damage. Let's say at a certain point in the game your boomerang does 200 dmg. 200x .03 = 6 . So best case scenario if you double hit them with boomerang, thats an extra 12 damage.

Compare that to warlord, and even early on in the game, the lack of a downtime and the similar scaling makes warlord better than spell and blade weaving, even with just 2 points.

Spell and blade weaving are meant for combo based champions like gnar, riven, lee sin, fizz, etc. To a lesser extent kayle, because you have to start giving up AP masteries, but when you are talking about masteries, you must always remember the opportunity cost of your choices.

Even on caster ad carries, warlord can be better even fairly early on in the game. Although, there are tons of people that swear up and down that warlord is a nub mastery. The problem with their math is that they assume the best case scenario for blade and spell weaving and they completely disregard the stronger late game of warlord.