Design for a phone with two bars on the way downtown, not the laptop on your desk
Your slowest realistic visitor sets the standard, and here that is a mid-range phone on a moving train.
Signal drops between stops. Pages that need three seconds of scripts before anything appears simply do not appear, and the person taps back to the results, where four competitors are waiting.
Test on a throttled connection rather than office wifi. The numbers most firms find are embarrassing, and the cause is almost always the same short list: a video header, a chat widget, six tracking scripts and photography nobody compressed.
Set a hard budget for the home page and the top three practice pages, then hold every new request to it. Marketing tools accumulate. Somebody adds a pixel, then a heat map, then a review widget, and the site gets a second slower every quarter.
Text first is not a compromise. A page whose words render before the images arrive is readable at the moment the reader is deciding whether to stay.