Its not as simple as that. The difference between 1x with narrow wide and and 2x is both should not be dropping chains, ever. Most people I know who fixed problems by going to 1x said something like "My new 1x is a vast a improvement over my x years old worn out drive drive line, ho ra for 1x hail the 1x....." (Followed no longer after by something along the lines of "Shut up about the 1x already"). These people also largely forgot they when their bike was new they never had issues.
Upgrading to 1x means a completely new drive line so of course it will work. Upgrading just the rear derailleur means just a new rear derailleur, so it might not work depending on the state of the drive line, especially the chain rings.
If you 2x is dropping chains, something is not setup ideally - worn components, adjustments or bad chain line. Upgrading to 1x will fix the worn components, but is most likely to make the chain-line worse unless you take great care or the BB has been changed on your existing setup.
IMHO provided you chain rings are in good condition, an XT clutch with new chain (and cassette if needed) will outperform you current setup of clutchless Deore. If you need new chain-rings, a 1x would cost a bit more, but would be a better way to go. The question you need to look at is cost - you could upgrade a few components to say XT level and keep the 2x, or deore level on 1x for similar money - which is the better drive line.