FlyerTalk Evangelist
Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: BA Silver, TK E+, AA PP, Hyatt Globalist, Marriott LT Plat, Hilton Diamond
Posts: 13,047
You can never really rely on "through checking" on different tickets.
It's an airline matter though, so KLM's policies apply, as they would be the originating carrier in Zurich.
But 1h 30m is simply not enough for separate tickets, independent of the luggage situation. If your Zurich flight is delayed, Delta are well within their rights to leave you stranded in Amsterdam, and you'd also lose that Alaska ticket...
P.S. Lufthansa didn't really through-check your bags though, as you need to collect your bags and go through US customs first.