You want predictable long-term costs
Webflow's CMS plan is $23–$49/month, but real Webflow sites typically need agency support too — meaning $200–$600/month for ongoing design changes. Custom sites at $250–$1,200/month all-in often work out cheaper, especially for sites that need active SEO/content work.
Your needs go beyond what the CMS models
Webflow's CMS is powerful but bounded — collections of items with fields. Custom code can model anything: complex relationships, conditional content, custom workflows, integrations that look natural rather than third-party-bolted-on. For unique business logic, custom always wins.
You want true platform independence
Webflow exports clean HTML/CSS — better than Wix or Squarespace by far. But the CMS, e-commerce, and most dynamic features only work on Webflow hosting. Custom-coded sites have no platform dependency; everything runs on standard PHP/MySQL anywhere.
AI search readiness should be default-on
Webflow can implement full schema, llms.txt, and AI-friendly structure — but it requires effort: custom code embeds, careful template setup, ongoing maintenance. Custom sites ship with this stack already wired in. For agencies that want GEO compliance by default rather than as an extra project, custom is the cleaner path.