I could get a decent car just for the advance payment on the Outlander that would last 3 years and probably be able to sell it
Sure, but you still have to keep in perspective that buying an Outlander PHEV on PCP would require a circa £5k deposit and monthly payments of circa £500.
Clearly if you buy a s/h car for £4k today, chances are that if it needs nothing more than routine servicing, you’ll be able to sell it on for perhaps a couple of grand. But you won’t buy a s/h Outlander PHEV for £4k – not even one of the early ones.