I agree with you, and you might have already noticing that Litecoin is following BTC. If we deeply look on to this they are almost identical this coin will gradually grow and by 2020 it might ready 100$ this is my personal opinion. For long-term investment it will grow and I am sure it will give great results.
If you've only started noticing this now then you must be really new to crypto;) Alts grow when Bitcoin does, this isn't news, this is already a fact of life here in the sector. I wouldn't say it's identical in the short term, LTC and other alts tend to have spikes and dips in their own frames. But sure, pull out the multiyear charts and we see practically identical patterns in alts.