I understand the concerns from a purist standpoint, but using this argument, then the Nova and Firestorm should be dislallowed as well.
You don't understand it at all I think. Nova & Firestorms are escorts. Strike Cruisers capital ships. There is a difference. It is even given in the Nova entry that they are under scrutiny from the Inq/IN/AdMech.
I would ditch RSV's all the way.
What is preventing me from fielding a fleet of one battle barge, three strike cruisers and 14 Firestorms? That fleet has 14 lances and is less than 1500 points! Firestorms and Novas are not going away- Firestorms in particular have been part of the SM fleet for as long as there's BEEN an SM fleet!
Not really, in Armada the option was to take pure SM escorts or RSV's. That was the first Marine list. If you ditch the Firestorm RSV option people can use them as Nova's. Just like people could/can use Dauntless light cruisers, or FW strike cruisers as marine strike cruisers. Just painted appropriate.
But, yes, one can take a Barge and only escorts, yes. That is cheesy and not fluffy. But possible indeed.
As said, there is a difference between escorts and capitals.
Another point that is not being brought up in all the vitriol about SM lances is that except for the SO, not a single SM vessel has lances that exceed 30cm. Why spend that many points on SM strike cruisers with lances when for just a few more points and a different fleet list you can have a perfectly decent Lunar, or even a Gothic if one is truly a lance hog? We're still tweaking this to make it right, but "SM's can't have lances" not a valid argument in and of itself, especially if we make them rare and expensive.
That's why it is a different fleet list (Armageddon).
Space Marines can't have lances is a perfect valid reason to dissalow lances to them. It is background you know. Just like you mentioned about Tau should be in background (although we differ on how to use that background as well so I guess we have different backgrounds.

, must be it.).
Still we wait views on:
- the refit we don't like.
- the seditio opprimere which should be dropped or changed (weapon batteries) because no one likes the ship. There is no majority which likes it.
- the 2nd shield on strike cruisers minus 1 bay
- your draft 'devestator' with too many bombardments