It's not just Space Wolves that hurt Orks, 5th edition and the new style of books gave Orks all sorts of problems, but them and IG do an excellent job making the problems Orks have that much more obvious.
The Ork armies Darkwynn (the overall winner) reported were Trukkspam (5 Nob units in Trukk, Ghazzy, Boyz in Trukks) and your generic horde. Both terrible armies, which appear to be a staple for 'Ard Boyz. Massed open-topped AV10, KFF or no, is not lasting at 2500 points, nor will 12 boyz.
Jaws is indicative of the overall increase in utility psychic powers have underwent, and Orks are stuck with no defense against it (other than the business end of a choppa) and our own psyker is, while amusing and fun, inconsistent at best. It's another nail in the coffin of "all your eggs in one basket" type armies, which Orks are infamous for.
The Ork Codex was the death knell of Tankbustas and Burnas, 5th edition just made it worse

If Burnaz could get a bosspole, dedicated transport, and +2D6 against vehicles you'd see them a lot more often. Tankbustas need Tank Hunters, a dedicated transport, and something for Glory Hogs (I propose a Ld test to encourage big units, big expensive BS2 single-shot units).
Orks hover in the same limbo that CSM do, they excel at destroying suboptimal, 4th editioney, crappy armies that noobs or people who don't feel like updating run, but when a solid 5th edition (mech typically, but there are alternatives) show up, they have a much tougher road. Orks really suffer against armor, and since it got more prevalent life got harder. For being lauded as a CC army, Boyz get slapped around regularly by stuff like Kroot, Grey Hunters, Assault Squads, Hormagaunts (especially the new ones, 3 attacks w/ re-rolls and 4+ poison is brutal) and suffer more from No Retreat! Nobs are cool, but powerfists see them drop like flies. Orks really lack a proper anvil unit like TH/SS Termies, all they have are hammers and units that specialize in killing basic infantry, but not heavier stuff or tanks.
Necrons got it bad, but Tau are extremely potent when done right. Unfortunately, since their book is so old they have like 1 or 2 builds to use, everything else pretty much sucks.
Cost effective in terms of points or money? Marines have the latter on lock, probably the former too. IG are great as well.
Orks are ==My== favorite army, I love them to death, but it's frustrating to be saddled with a book that was basically outdated before the ink was dry. The worst part is that nobody sees it. Since tournies today are so comp-heavy, all you see are crappy armies and when it comes to poor lists, Orks dominate against them. It's gonna suck for people when the rug gets pulled out from under them, Tyranids may be the ones to do it too
You can make Orks work, just like any other army, but they are really limited. Still a ton of fun to play, though.