Q: “If telemetry tells me I’m over-braking for a turn, but reducing braking creates understeer, is it a steering input issue? To clarify, reducing braking causes me to miss the apex. What is going on here? Do I stink at turning in?”
A: I don’t smell anything, so I don’t think you stink! J
When you say you reduce your braking, I’d have to know where you’re reducing it. If you reduce it towards the EoB (End-of-Braking), then it might be that you’re unloading the front tires too early, and that’s what’s causing the understeer. If that’s the case, then I’d suggest moving your whole braking zone further into the corner – beginning and ending braking later. In doing so, you’ll be trail braking a little more, keeping the front tires loaded a little longer.
The way you describe it, you’re releasing the brakes early – and you’re doing that in an attempt to not over-brake, but it’s causing the understeer. If you move your whole brake zone in further – a later BoB and EoB – then you’ll carry more speed into the corner (not over-brake), and keep some load on the front tires. That’s the first place I’d suggest working on.
From what you say, I don’t think you’re over-braking, but you’re over-slowing. And that’s because you’re beginning your braking too early. Move the whole brake zone in, and I suspect you’ll carry more speed into the corner, and have less understeer. This is a case of getting a double-whammy working in the right direction for you!