In particular, data transfers are not limited by protocols used to transfer data. For example, we use the same TCP/IP whether we were on 28k US Robotics modem-based connections transferring at 2-3KB/s or now on fibre connections transferring at 10-100MB/s. The usability of the protocol is not limited by the speed or bandwidth of internet connectivity.
If we consider the whole universe of computers connected by TCP/IP, then I think network effect is also present in these simple networking protocols. You can do more with TCP/IP if there are a lot of other nodes which can send/receive/transmit packages.
With Bitcoin as the money protocol, I think the size of the value transferrable is dependent on the size (value) of BTC relative to e.g. USD. In other words, the usability of the protocol improves as the amount of value that can be transferred over the protocol increases. Hence, as BTC price increases, Bitcoin as the money protocol also increases in usability, which in turn increases the demand for BTC, which in turn increases the usability of the protocol, and so on.
There are lots of Bitcoiners who believe in that causality (basically Metcalfe's Law or "the network effect") or a variant of it, and the whole Stock-to-Flow "theory" (which I consider pseudoscience*) is built around that assumption.
But there are some flaws. For example: Bitcoin may be the premier protocol, at this moment, to transfer value without centralized intermediaries. However, for many use cases, intermediaries aren't that much of a problem. Or may even have advantages, for example regarding compliance. Additionally, you can introduce very slight variations into the protocol and the "value" system completely changes. The Litecoin protocol for example is basically the Bitcoin protocol with very small changes, but leads to a whole new "value system". Ethereum's protocol is a Bitcoin protocol with more changes. More Litecoin or Ethereum transactions do not mean an increase in Bitcoin usability, even if the protocol is very similar. At the contrary, it can create competition and fears that Bitcoin's advantage is decreasing, leading to price drops.
So while Bitcoin undeniably is a protocol, its value system is a bit detached from it. And there is fierce competition, both inside and outside the cryptocurrency space. We still don't know if Bitcoin can really become the premier universal money standard protocol.
And thus its price discovery will be quite erratic, and it can even fail completely,
until it's used more "as a currency".
I'm however optimistic that Bitcoin can see much more adoption than now, even if it doesn't become the "universal money standard" protocol: Of all money protocols without a central intermediary, it's the most secure one. Most altcoins are vulnerable to 51% attacks or PoS Nothing-at-stake-style attacks. This sets it apart from coins like Litecoin and even Ethereum. In the long term a Lightning channel or a sidechain account can become the standard "account" for people who can't or don't want to open an account at a bank, be it because they don't want to trust a bank, or because they're not accepted by the banks, or because they need to stay away from the KYC world (e.g. dissidents in dictatorships).
* See the following discussion:
https://bitcointalk.org/index.php?topic=5191012.msg59101466#msg59101466