Your store feels slow. A tool gives it a disappointing score. Someone suggests installing an optimisation app.
I would first ask something else: what is actually making the shopping experience slow?
It matters, because the culprit could be an image, a pointless script, a heavy feature or inefficient theme code. Each one needs a different fix. A new subscription is not automatically the answer. Least of all a subscription that adds more JavaScript to a page that has too much JavaScript.
Separate the symptom from the cause
Describe what happens. Does the first product image arrive late? Does the size selector stop responding? Does the page jump around while it loads?
Those are different problems. Core Web Vitals cover loading, responsiveness and visual stability through LCP, INP and CLS. A Lighthouse score is useful diagnostic information, but one simulated test does not describe every visitor's experience. It describes one visitor, in a lab, on a good day.
Use real visitor data where you have it and repeat controlled tests on the relevant pages. If your store has too little traffic for a reliable field report, say so. Honest limits beat a confident guess.
Test the templates customers use
Do not stop at the homepage. Check a collection, a typical product, a product with more complex options and the cart.
Keep the test conditions comparable. Record the URL, the device conditions and the theme version. Otherwise a different network or a different page can look like an improvement you made, and you will feel very clever for a week.
The goal is a baseline you can return to after every change.
Inspect what the page downloads
Large imagery and unnecessary JavaScript are good places to start. Check whether images are sized appropriately and whether tools load on pages where their feature is never used.
Shopify's theme performance guidance recommends keeping essential content in Liquid and HTML, and treating the main visible image differently from the images further down the page.
That does not mean removing every useful feature. A sizing tool may earn its place if customers need it. A hidden widget that loads across the entire store deserves a harder question: what exactly are you doing here?
Look at behaviour, not just file size
A small script can still do expensive work. A feature can keep updating the page, fight with another component or delay the response to a click.
Reproduce the issue with browser tools, then isolate the suspected dependency in a duplicate theme or a suitable test environment. Change one meaningful variable at a time. Changing five things at once is not testing, it is gambling with extra steps.
If removing a component improves the test, check what you lost. Reviews, consent controls and product options exist for a reason. Replacing them needs a functional decision as well as a performance decision.
Protect the shopping journey during fixes
After a change, verify product options, cart updates, navigation and the handover to checkout. A faster page does not help if customers can no longer select the right item.
Record before-and-after evidence without promising a revenue increase. Performance can influence shopping, but so do pricing, traffic quality, product fit and delivery expectations.
A useful report says which pages changed, what was measured and what is still unresolved. It should not just show a green circle. Green circles are nice. They are not evidence.
Do you need a new theme?
Sometimes. If the theme is hard to maintain and carries years of conflicting changes, rebuilding can be sensible. But a slow store alone is not enough evidence.
Start with an investigation. Then choose between targeted fixes, a theme upgrade or a larger rebuild once you understand the constraints.
At Athom, I work across storefront development and the systems connected to it. Discuss Shopify performance and troubleshooting, or view the available audit services for a structured starting point.