I agree with your thinking, that's why I thought of this build:

To make up for Medusa's lack of mid game damage and lockdown, I build aquila, phase, drum, sometimes a wand. After these items I will go situational. Usually I like to grab a yasha because she can farm it easily, and it will help her movement speed, surviability, and damage all in one low cast package.

After that, if I want survivability I get both linkens, skad. This will slow down the game if I play correctly, because Medusa will kill creeps insanely fast and be very hard to kill (unless they have certain mana drain or high burst damage combos). This build lets you become a strong defender with good late game capability. You will eventually sell those mid game items like phase, aquila, drum, for travels, mkb, daedelus, or butterfly. But if I want more damage after mid game, I will usually go straight into sange and yasha into another damage item like mkb, daedelus, manta, butterfly. SnY gives Medusa good stats and movement speed. You have already decided you don't need as much survivability, so mana shouldn't be an issue.

She farms fast enough to get those initial items up before mid game team fights start breaking out, and you can really have a lot of control over how the fights go with your ult. Keep in mind, she relies a lot in teamfights for her teammates to have good lockdown, otherwise she is kited very easily until she builds something like skadi and mkb. If this is the case, you want to sacrifice teamfights for pure farming and pushing. You can force tps quite quickly, and back out safely with ult/tps if you have to. I think getting items like aquila/phase/drum/yasha are often critical on her. She lacks basic control outside of her ult forcing people to avoid a certain area for a moment. She also benefits a lot from good regen and high stats, especially if you cannot land well placed mana drains with her snake. These items compensate well for that, while also accelerating her farm.

Anyway, that's how I've been playing her lately, and I'm finding a decent amount of success. The games will go worse if my team lacks good lockdown and some early to mid game support, but that's often how it goes. Dusa club!