I am not really sure. When I used special weapons Regiment I would primarily used it for the "Boys Tommies" that combine decent AI and decent AT. I found them quite effective especially once the grenade was unlocked for the early game.
Now that would open they using more Ro.E. in the army composition that could later be equipped with AI weapon since the AT department is already covered.
Now I have not tried this build recently but it had some success when I used it. I guess will have to wait until some top player give this build a try.
He uses two Bren commandos as main AI and does not even clearly favour anvil. Clearly the AI in this build mainly comes from other sources than REs for the most part of the game.
Also don't forget he is not talking about REs, but RERs, which come with 5 men from the start of the game and a potential flamer unlock.
In summary, the builds are very different and you can't directly assume that REs can work because RERs potentially work in a completely different build.
The problem was not only the fire power itself but the combination of high far DPS and decent close DPS.
If you like another example you can check PPsh conscripts that combine bolt action rifles and smgs that have little synergy.
I am point out this because I have read the "synergy" argument before.
Conscripts fight best against Axis infantry in close range, that's their best chance to win early on. Anyway, this comparison is apples and oranges. The PPSh upgrade gives you 4 PPShs, leaving you with only two Mosins, that, remember, still have a rather short range focus compared to all other Rifles. Do you really want to compare this setup with a weapon setup of 3 dedicated long range Rifles, 1 long range LMG and one short/mid range LMG? This does not make sense. Also all of this is neglecting that Conscripts have ourah to close in the distance, like many other squads with shorter range focus.
Vicker K will not turn IS into riflemen. What it will do is give them better moving DPS than Bren tommies and better mid close DPS.
Now if that is worth the extra mu is another question that I need more data to offer an opinion.
At this point I would have to say that is probably situational.
If the 0.25 accuracy multiplier is true - which seems to be the case at the moment - the moving DPS is not a reason at all. You'll do way more damage just staying still and using the Bren and thereby actually both Brens and all Rifles to the fullest instead of using the Vickers and three Rifles on the move. Even the normal Enfield will give you better moving DPS for almost all ranges.
Better close to mid definitely, but probably not worth it for IS. You need long range DPS for defensive play, especially if your opponent has long range specialists by default. Otherwise you'll just be out-traded every time.