I think MANX2 were basically a travel agent selling seats on aircraft they leased.
How would 'regulations' affect operators such as Thomson, how would airlines lease-in capacity for short term contracts, or once-off substitutions like Titan do on occasion for Aer Lingus? I don't believe that Aer Lingus, Aer Arann or Titan are inherently unsafe airlines, just because they lease aircraft to each other. It is possible that Flightline BCN were less reputable, but that is down to regulation from an operational point of view, not marketing, specifically the Spanish authorities.
Whatever the outcome, the report should be interesting reading.
3 companies were involved in the operation of Manx2 services (them included) - You had Manx2 the ticket seller (thus not liable for anything bar customer to finance), Flightline BCN who provided the AOC, and Air Lada the plane-providers who employed pilots. And last I heard the AAIU and EASA had serious trouble getting information from the latter.
BBC Spotlight pursued Manx2 who said they couldn't comment on a investigation (but outside of that rejecting any liability when victims pursued legal action), Flightline BCN told Spotlight the company had no responsibility for the accident. They also repeatedly tried, without success, to contact Air Lada.
In the above examples you've pointed out, they involve two companies, quick leases are known as ad-hoc operations and thus the operating carrier (say Titan) has operating liability where as the leasing party (e.g. Aer Lingus) still bare responsibility for e.g. refunds, compensation and the financial operation of the leased aircraft (its costs) - That's why those leases are all above-board and excellent response in situations of sudden disruption. The Manx2 business was so much more complicated and involved lots of smoke screens we'll read more about that.
I think questions need to be asked also (hopefully the final report can clarify it) why the EASA banned Flightline BCN from operating Fairchild Metro IIIs 2 months after the accident and not before, the agency is there to prevent such incidents and failed in this regard if it found it necessary to ban the carrier from operating the aircraft type. They clearly found something after the accident.