You hit the nail on the head, the challenge with Blockchain and Bitcoin is that it did two things, which together were supposed to tackle the original problem, peer to peer monetary exchange without a trusted intermediary.
So for that the blockchain provides the trust mechanism which is useful. However, the blockchain is just the channel, it needed a medium of exchange, you couldn't very well use USD because then you are back in the banking system.
Here, BitCoin is introduced.
However, the problem with BitCoin is that it initially has no value. So if I bought a nice coffee mug for $10, and I wanted to give it to you for BitCoin, well your BitCoin is currently worth nothing, so we can't have an exchange.
This is where the scarcity argument for BitCoin comes in, which is supposed to inflate the value of the currency, because it is limited. You can also see by the amount of BitCoin initially envisioned the scale of how large the peer to peer exchange network was supposed to be.
We are used to paying $1 for coffee, but are you used to paying 0.0000000001 BitCoin for a coffee?
Now absent speculation, the price of BitCoin would be reasonable, and determined by the effort of the miners, since they are exchanging their fiat currency for computers and energy, and that creates a stable layer for the price.
It would also stand to reason that until all of the Bitcoin are mined the price would continue to increase, because the amount of energy used to mine them increased, while the supply was limited.
If instead an equal output of energy produced and equal output of BitCoin, then BitCoin would have a stable price, that would track energy prices globally, and then the coin would have value because it would still take work to produce it, or you can simply purchase one if you don't want to waste the time mining it yourself.
And you can pay a premium for that already mined coin because it's more convenient.
It's also important to note that the system was already incentivized for miners because they are the ones processing transactions and they collect a fee. So if mining produced a 1:1 BitCoin exchange for fiat currency based on energy usage they would still make a profit from transaction fees like VISA, or for selling the BitCoin for a slight profit because some people wouldn't want to setup a miner themselves, or wait for their coins to be minted.
Speculation occurred because of the limited supply and the increasing difficulty of mining, absent those two things, the value of BitCoin once established would actually be very stable and could in essence become a medium of exchange.