Contest or pivot

Two players on the same carry draw from one pool. Every copy either of you buys is one the other can never find. So the question is not only whether someone else plays your comp. It is how many copies are left, and which of you is closer to the upgrade.

Count it. There are 10 copies of each 4-cost, and a 2-star holds 3. Two other players with a 2-star each leave you 4. A 3-star takes 9, so it is gone, and even your 2-star now needs 3 of the last 4. Cheaper carries have deeper pools: the same two 2-stars of a 3-cost leave 12 of 18. The 3-star is still possible, but reroll comps need it, and every copy on another bench costs them more gold to find.

The lobby keeps the score. In ranked games, boards whose carry nobody else built average 4.4. With one other player on the same carry it is 4.7, with two 4.8, and with three or more 5.1.

Contest when your spot is clearly better: you hold more copies than they do, your items fit only this carry, or you have the gold and the health to roll first. Then roll sooner rather than later, because the copies go to whoever finds them first. Two players who both keep rolling for the same unit usually both end up short.

Pivot when you are behind on copies, or when your items fit another carry just as well. Pivot early, and along what you already hold: a carry that uses the same kind of damage items, units you already have pairs of. A line nobody else wants often beats a stronger comp you have to share.