You're right, that is surely a thing you do not want to do yourself. This is why Baqend does all the browser and CDN caching, TTL estimation, query invalidations and so on automatically.
In terms of the frontend if you do not want to rely on a stock theme - and many larger ecommerce site won't - then you will have to do these optimizations yourself. Fortunately with good tooling available as outlined in the article.
I think Shopify is in fact a great improvement over systems like Magento. But if Shopify is well-enginneered (which I'm convinced of), how do you handle sudden load spikes in the database? Do you reshard and migrate data in real-time? How does Shopify scale the application tier? How can tenants run scalable custom backend code? What happens if a database or server node crashes?
The advantage of Baqend is that its inner workings are published in research papers and blog posts, so people can judge the performance and scalability not only through benchmarks and real-world examples like Thinks but also by looking at the design.
In contrast to Shopify, Baqend is backend-as-a-service which means customers have full freedom on how they design their site or shop. They do not have to live with a server-generated HTML that they cannot change - they can for exmaple easily build a React/Angular single page applications, run server-side JavaScript code, do custom queries, build a native app around the same business logic and APIs, subscribe to websocket-based change streams etc.
While I respect that it took you 10 years to build Shopify, this is usually not an indicator for scalability and a low-latency design. Often such projects end up with solutions like MySQL sharded at application-level, intermingled technology stacks and legacy systems.
Disclaimer: I'm the Baqend CEO and its caching approach is my PhD thesis.