Another way to do it would be to include some Long Fang units in the formation.
Now that would be a solution I could get behind... no devestator formation, but the ability to add Long Fangs in limited ammounts to other formations, complete with extra shots etc, to help compensate for the lack of shooting from the rest of the formation...
Having a rule in WH40K saying that Grey Hunters don't have Heavy Weapons (another WH40K abstraction!)
How is that an abstraction?
It's a rule that says 'Grey Hunters eschew Heavy Weapons and instead take an extra Special Weapon / Long Fangs are the only Space Wolves that use Heavy Weapons'.
It's no more an abstraction than saying 'most marines use Boltguns', or whatever.
does not necessarily mean that Grey Hunters in the 40K world don't have or use them.
Unit writing for Epic is all about writing a set of unit stats that picks an abstract for what is most common.
Thus all Leman Russ have hull mounted lascannons, and all Devestators carry Missile Launchers.
What they don't do is give all Leman Russ hull mounted assault cannons, or all Devestators Heavy Stubbers...
...which is effectively the same thing as saying 'Grey Hunters should have missile launchers'... the fact is, they don't
Whilst 1 in 1000 Grey Hunters might technically possibly maybe carry a missile launcher, that is not a typical Grey Hunter weapon...
...and that's where the abstract
comes in, to say that you should represent the most common equipment style.
So your Long Fang unit gets Heavy Weapons (and justifiably, more of them than a Devestator unit), and your Grey Hunter unit gets no Heavy Weapon, but does get a Special Weapon... because 99% of Grey Hunter units will fit roughly under that template, and we can forget about the 1% that featured in a Black Library book one time carrying a Heavy Flamer.
Sure, the fluff will flow to make people buy all the new minis, but we can simply choose to ignore it
Yes, you can ignore the background, or create a list based on background that comes from a ten year-old book that has been overwritten... either way, you're effectively making up your own 'Space Wolves', instead of writing a list that tries to reflect what 'Space Wolves' actually are.
There comes a point where you willfully ignore so much background (or 'fluff', if you prefer) that you end up playing a game that looks nothing like the background at all...
...in essence you create your own game, which whatever its merits (and they may be legion), is not set in the Warhammer 40,000 setting anymore.