An e-commerce brand on Squarespace was leaking 2.1% of revenue to a checkout it couldn't customize.

An e-commerce brand on Squarespace was leaking 2.1% of revenue to a checkout it couldn't customize.
They did $600k/year on Squarespace Commerce. Their checkout had a 1-page flow they couldn't touch, no upsell, no address autocomplete, a known abandonment point. They moved to Shopify, added a tuned checkout with autocomplete and a post-purchase upsell. Cart-to-purchase conversion rose from 1.9% to 2.4%, and average order value climbed 9% from upsells. On their volume that's ~$54k a year recovered. The builder that 'just works' for content can quietly cost you a salary at the checkout.
Agree? Or am I wrong?