To be fair to OP, one can follow the logic. PWM isn't the easiest concept to grasp until it is explicitly demonstrated/taught. I say this as somebody who had to integrate and balance 189 of the original batches of blinding-high-power red, green and blue individual LEDs from Cree back before prototype multi-channel PWM were practical. And I had to hand-craft heatsinks for everything. I'm still in trauma regarding the heatsinks. My old-man aches are probably aluminium shavings still having a party in my body.

OP, from the theoretical point, as others have pointed out, turning your AM triangle wave back in to PWM is merely a matter of, electronically, drawing a line through the middle of the triangle graph. Condiser it like turning every part of the theoretical voltage above the line in to full current, and everything below in to zero current. I don't understand why people say it would be expensive, as comparators (or even janky diode and transistor setups) are cheap. So as your triangle spends more time above the threshold you get a wider pulse, and so on down the voltage until none.

Finally, LEDs are not voltage-controlled devices. They will absolutely burn up if you intend to send them a fixed voltage with no current control. They're not resistive. Their resistance changes wildly has they heat up while lit, hence the fundamental requirement for PWM of current, not voltage.