2 part post: first is some response to what you said on magister, second is a much much longer post about skilling supplies in pvm.
Note for potential bias: I am comped, own a blue party hat i bought for 14.3bil, and own all t92s/high level armor, I spend about 95% of my time pvming, other 5% keeping my comp cape
Magister related feedback--
-soul fragment=pet, you can't put the boss in your slayer dungeon
-fyi tormented demons are a slayer task-you can persuade morvran/kuradal to assign them to you after completing while guthix sleeps
-magic preferable if doing 4tick aa, ranged is fine for casual kills, melee also works-bomb has timer thats easy to avoid, barge back in
My thoughts, from around 150kc at time of writing this
-was shocked how easy it was for dropping t92 weapons, managed first kill 1:23, now consistently gett 55 seconds-1:05 (i use 4tickaa)
-the drop table is the worst of any boss i can remember on release for the supplies it costs since i can remember playing the game, from where i bought keys i lose around 1.5m per kill, would be around 650k at current key prices
-mechanically super boring, feels like fighting a dummy-assuming you dps hard enough you SKIP all minions, so really the only mechanic is the barge (hits fairly hard, but can be predicted by chat so you can flick pray melee) and the bomb with a fairly lengthy timer
Re: skilling supplies-a boss like this has never dropped SO FEW quantities of skilling supplies--even qbd brings exponentially more, if your position is hard line skilling supplies always bad, i guess fine--but, consider what it would be like to train 120 herblore if the ONLY source of herbs was farming, could be nice for the production side, but the consumption side would be brutal
Concern over batttlestaffs and rune bars makes literally no sense to me. Battlestaves will never fall too far below their alch floor of 7k gp, arguably bstaff drops are bad because they devalue the rewards for elf city/varrock tasks (bstaff purchases used to be good money, now they are dead even or a slight loss if you nis staves on the ge).
For rune bars, I'm going to assume your argument isn't really about rune bars crashing-their alch floor means this can't occur. I'll assume instead your argument is that smithing rune bars should be profitable (also guessing you want runite ore removed to get people mining rune again, but lets set aside the fact that if this happened rune ore and rune bars would theoretically both rise at the same rate). Nobody has made rune bars from rune and coal for a decade, when would you ever do this? I'm kind of confused. Aside from there already being a massive amount of rune bars in game that come from other methods, even assuming we remove all rune bars from game, is the cycle of buy rune ore and coal from ge, get people to go to blast furnace, make your own rune bars, then either smith for xp or sell from profit really a model for skilling anyone will enjoy? On the profit side, the difference between rune 2H and addy platebody is rather marginal, so then you'd have to remove all rune bars and all addy bars, which I guess is OK but within the current framework, that would mean smithing would cost an exorbitant amount, or you'd be at the blast furnace.
Lastly, EVEN IF you think a return to 2004 is desirable, which is fair enough, things like seren stones, sandstone, corrupted ore etc exist, which means people will use those methods even more than they already do. Corrupted ore is far faster than making rune bars in terms of xp, and even if it was profitable I doubt it'd be worth it.
"replace skilling drops" is not so simple, few examples i commonly here:
-herblore-farming has NEVER been the primary source of herbs coming into the game (bloodweed is exception), the skill pre-dated farming and things like chaos druids were always a better source when it did come out, you are right that herbs don't sell for what they once did, and maybe mass noted herbs is part of that, just remember that the fewer herbs come into the game, the more expensive herblore gets, and the price increase of herblore will always outpace the profit of farming. Furthermore, the player base is aging, more people are hitting 99/120/200m herb (whatever their goal is) every dxp weekend, which i suspect is also a major contribution.
-energies--this is more reasonable, i guess, i will say the rate of consuming energies vs rate of obtaining energies with pvm isnt even close. if i do 10 hours of aod the cost in drain rate is so much higher than the number of energies i require its ridiculous. Remember that a pvmer with the same number of charges as a skiller with say a augmented crystal hatchet and augmented excalibur will last the pvmer 7-10 hours and the skiller 300. PvM is EXPENSIVE.
-things with an alch floor--bars, rune ore, bstaves etc. Maybe mining/smithing rework will change things, outlined above why i don't think this is a relevant change.
-summoning supplies-what are the alternative methods for bringing things like water tallys into the game? Maybe it would be better if summoning costed 3, 4, 5 times more--no strong opinion here.