It gets its USD value from BTC
That's the definition of "alternate" coin, it will never be a primary, ever. Actually, it's impossible.
That's not true. It is weakly connected to BTC. When BTC falls momentarily it also falls because BTC is the main cryptocurrency and when BTC price falls all cryptocurrencies also fall because BTC represents them.
However, besides being cryptocurrency, LTC has other benefits which are different from BTC. And that saying, it value against BTC grows over time.
Look at precisely one month ago. LTC was about 0.01 BTC. Now it's 0.03 BTC.
So, the bottom line is that BTC price certainly affects LTC price for the reason of both being a cryptocurrencies. But it's not the only reason of its price. And the other reasons affect value of LTC independent from BTC.