LTC got to within 20% of BTC on a price basis briefly (market cap was smaller since LTC is newer but that's a relatively small effect), and there was no real threat to Bitcoin there.
Because it was the best coin for GPUs to mine for a while after ASICs banished them from Bitcoin (so all that BTC discarded hardware value was infused into Litecoin), then afaik the speculators piled on to the ramp up (remember people looking for leverag over BTC in the 2013 run), and when that ended (and with ASICs for Litecoin) afaik it cratered (haven't been watching lately).
And this is a critical point. If you can move the worlds CPUs into your coin decentralized, you can beat Bitcoin because you can move more hardware value into your coin. Especially if you can give the mined morsels to be so small that no one sells and they instead circulate those morsels on a use-case that Bitcoin can't do.
Why do you think I expended so much effort perfecting a CPU (ASIC/GPU resistant[1]) hash that I believe is
far superior to Monero's (you can verify or refute if ever it is released).
[1] I mean not more than 10X efficiency advantage for an ASIC.