Layer2 networks have tremendously taken the load off of Bitcoin and Ethereum since the last period where fees were sky high. It's been almost 2 years since then and scalability solutions have only improved across the board. Unless a unique kind of attack spikes fees in a way that can't be mitigated, I'd say it's unlikely that fees will ever become as unbearable as they have been in some periods of the past.
Layer-2 solutions probably play a significant role as far as the Ethereum network is concerned, but probably not that much when it comes to Bitcoin. The Lightning Network only holds a few thousands, right? As to sidechains, Liquid has also a few thousands, if I'm not mistaken.
In other words, I think they're not really the reasons why Bitcoin's network is now free from congestion. For one, it's the absence of spam transactions. Secondly, I think it's the kind of adoption Bitcoin has today. It's institutions, OTC, ETFs, IOUs, paper Bitcoin, centralized exchanges, custodial wallets, and the like that have become the ruling standard.