Yes, I think the core problem is bitcoin’s proof of work that requires the creation of new block (on average) every 10 minutes. As more miners want to get rich doing the mining, the average payout per miner will get smaller. In theory, there will be an equilibrium point where the cost of mining is worth it compared to its rewards. But in practice, what this means is ever larger mining operations, specialized hardware, and the incentive to get “free” electricity (usually by stealing it). I don’t see this changing any time soon.
Another cryptocurrency I’ve been following for a while is Stellar. They focus on currency exchange, but their blockchain can theoretically be made generic.
They use a consensus approach, whereby new ledger entries are added and approved based on how many other people in your trusted network also approve the same entries. It turns out that it is way faster than mining and way less energy intensive.
Though the true bitcoin enthusiasts hate this model because it can lead to some amount of centralization as the most trusted nodes turn out to be real world entities like banks and government institutions.
But, they also seem to have no problem with the centralization of bitcoin mining happening primarily in China and sometimes by shady operations stealing energy from the public.