I watched an Andreas Antonopoulos video recently that explained exactly why it doesn't really matter if slightly more efficient projects emerge. He compared it to introducing rabbits to Australia. Now there are rabbits everywhere; they found the niche in the environment and their population exploded out of control... you can't uproot them by introducing a slightly more efficient animal; they're already entrenched into the environment. Bitcoin is also entrenched. It was never supposed to be the best solution or even a good solution. It's "good enough". That's all you need with first-to-market advantage.
Also all these other coins that come out aren't superior to Bitcoin in the least bit. There are trade-offs, and these other coins are sacrificing some other vital attribute in order to achieve higher scaling, throughput, and efficiency.