Midas gives you a level advantage across all the lanes - you're not just beating the offlaner and magnifying early gpm, you're also ~2.3 levels ahead of both mids and their safelane. The immediate level 2 means you have a silence and a slow on drow, a slow and metamorphosis on tb, both forms on troll and his nuke/slow. This is an immediate advantage in and of itself, and already helps you zone an offlaner. I think the issue here is that your solo kill potential as a level 1 carry with lothars against an offlaner is quite a bit lower than you think. Drow is still far from guaranteeing a level 1 solo kill with just lothars - in a solo lane it's not enough, in any halfwit trilane it's not needed to zone. Shadow blade improves your kill potential much more later, when you have levels in silence, your ult, and enough attack speed/levels to kill the target during the silence. Having it at level 1 isn't as good.

Would you rather be 2.3 levels ahead everyone by 3 minutes into the game or have the ability to completely zone the offlaner? This shouldn't even be a serious question for most people. The latter actually happens in some games and people can just sac the offlane. I'd rather have level 3 frost arrows and ult by 3 minutes and have supports zone before then, than I'd have a shadow blade to zone the offlaner maybe 2-3 times - even if it does result in a kill, he forces supports to stay in lane after knowing you're out of mana, and you're not really beating other lanes with this, which you really need to do considering YOUR TEAM HAS NO GOLD.

you've been jumping from point to point like an child - at one time you tried to suggest you get level 6 much faster with kills than midas, another point you tried to say the offlaner has no escape, another point you insisted it's even a 3 shot kill and that drow should roam with the early lothars into other lanes to find a kill at level 1-2 instead of farming. All of these seem to tell me you're not very good, or even interested in being good.