> It will cost you 10x what you’re paying now, it will be much more brittle and harder to fix.

I say this as someone who's done a lot of freelance work: No, you can't bullshit your clients like this. You may be able to tell them that if it's not an actual lie, but in your case, if you actually would endure such costs and fragility, it speaks volumes about your agency's skill levels.

If you're in the business of selling websites, maybe it's time to actually learn how to write a good SPA rather than bury your head in the sand, because yeah, clients do actually want those.

10x the cost!? Well, I have a quote from your competitor that's a fraction of that amount. If you keep quoting unreasonable prices, perhaps I should rethink our business relationship and move elsewhere.

Sure, you can say that. You will lose your clients to the agency down the road who happily use React and say "no problem." Especially once it turns out that it _doesn't_ require 10x the time and budget and your prospective client tells everyone you bullshitted them.

...and it breaks linking to URLs and backspace.