Yes you've got it. Tbf to QR, barring perhaps AY's Platinum Wing in HEL, BA's CCR in LHR T5, the status-based Platinum Lounge is probably far superior than 90% of oneworld lounges out there globally IMO (with the other 5% being QR's outstation Premium lounges at LHR, CDG, BKK, SIN and the other 5% being split amongst QF F and CX F lounges probably), certainly better than any AA lounge or BA outstation lounge! Yes it isn't quite to the scale and grandeur of Al Mourjan or Al Safwa, but it is decent.

Coming back to your original query - yes, you have got that right. Al Mourjan and Al Safwa are only for ticketed oneworld (eg. BA Club World or First, RJ Business would allow access) First and Business class tickets (award flights also count). The exclusions to this are:
1. Operational upgrades
2. Upgrades done through QR's promotional offers sent via email or QR's Manage My Booking (a BA online or airport upgrade solely for a BA operated service would still be eligible for Al Mourjan and Al Safwa). An upgrade done through a ticket reissue/fare class change that results in your ticket moving to a new fare class altogether (typically done by paying any change fee + fare difference) would be eligible for access though
3. QR 157 stock P class "Business Lite" tickets (any other oneworld airline stock QR operated business/first ticket would permit access to Al Mourjan/Al Safwa respectively)

However, irrespective of whatever type of ticket you have, as a oneworld Emerald passenger, you will always have access to the Platinum lounge or any other non-QR oneworld lounge globally. So whilst it's not the ideal scenario, QR is till honouring your status and giving you status benefits (namely extra baggage allowance, lounge access in some form, complimentary seat selection, priority security where available, priority boarding and priority check-in).