Sure, the AMP page looks much cleaner because it lacks the ads, side bars, and other junk that the Washington Post puts on their normal page. But they want that junk. If everyone on laptops and desktops starts using your trick, the Washington Post will adapt and find a way to put the same junk on the AMP page. Then we're back to square one.
As far as I can tell, your method of viewing a nice clean page depends on your trick not becoming popular!
Safari reader-mode can be activated on the normal page of the Washington Post when it is loaded half-way. Reader-mode discards the ads, side-bars and other junk anyway. IOW when activating Safari Reader-mode as soon as Safari allows, the AMP pages loose a lot of their benefits. Combined with ad-blocker and a proper image compression probably little benefits remains for the end-user.
Startpage.com delivers the same results google.com does. I've never hit AMP pages, so I assume they neither they redirect to AMP pages, similar to duckduckgo's !g.
edit: This is with an ad blocker on though.