My '14 FXT was recalled for LSPI...even before that I was aware of the issue and poking around on websites (including this one) to try to find oils that would make that destructive event less likely (mostly M1 at the time). I know that Subaru has adjusted the engine control software in an attempt to minimize LSPI, but I am still concerned about the issue.
Luckily, the motor oil industry has responded to this challenge and we can just look for oils that meet the SN+, dexos1 Gen 2, or Ford -B1 standards that have actually been tested for LSPI mitigation.
If you like Castrol, you can certainly find 5W30s in their line that are SN+/d1G2. I don't know about Motul or LiquiMoly, Ravenol has at least one d1G2 5W30 (DXG) but it is quite pricey in the US.
I decided to try something with a higher HTHS for this summer and just put in SN+ M1 10W30 HM, which is 3.5 compared to 3.1 for M1 5W30 and also has 7.6% Noack loss per a poster here who contacted XOM...but, you say you don't like M1.
Valvoline Advanced Full Synthetic has a high HTHS for a GF5/SN+ oil (3.2) and also a pretty low Noack loss of something like 9%, plus it has also met the d1G2 standard for some time.
Enjoy your '18, looks like that is the last year for the FXT for a while. Subaru is bringing out an Outback XT with the 2.4l DIT from the Ascent for '20, maybe the FXT will be back before too long!
BTW, for some of the other posters, the '14-'18 FXT has the FA20DIT engine.