Both ways of doing raids are utter shit and I generally can't be bothered. You either get a bunch of randoms from Recruiting and maybe a few friends to do them, which can succeed but obviously is quite likely to fail; or you get a dedicated VoIP group or even join some raid-centric clan that practices regularly, which really isn't worth the trouble.
Nightmare raids have much higher drop rates for the non-shit Arcanes, and they're much more easily screwed up. Most Warframe players suffer from turbo ADHD and autism, are extremely impatient, and don't want to teach anyone new... so when raid groups do manage to form, get good, and meet regularly, they often become secretive for fear of novices trying to come along, in many cases seceding from whatever clan they're in and presumably quit the game eventually because "raiding" in this game is extremely gimmicky and one-dimensional, and there's really not much of it.
In terms of the platinum to be made from Arcanes, your time is just as well spent farming up Prime sets to sell so that you can use that platinum to buy Arcanes from raiders.
I'm well into MR21 and I still don't have Ash, either. Other than Excalibur Prime, which is unobtainable, Ash is the only frame I don't have, despite the deaths of many manics when I ran through LoR a number of times.
Ash really isn't something for newer players to just farm from raids, because you are expected to have certain setups, primarily max-range efficient crowd control such as Radial Disarm, Prism, Avalanche, slow M Prime, and so on.
Besides which, Ash isn't called trAsh for nothing.