I think Sessions recusal was well taken. He has a conflict investigating the campaign.
The problem here is that Roesenstein and Mueller (who arguably are the right people to be in charge of whatever Sessions recused from) are handling cases that Sessions is not recused from - but they keep him out of the loop just like Comey, Strzok and McCabe kept the straight arrows (Priestap) out of their "get Trump" loop.
A problem of its own right is Mueller taking on "obstruction." This is a problem on several levels. All evidence is that Trump did NOT intend any investigation to stop as a result of firing Comey. No effort made to interfere with DOJ working. Trump has this power, using it is his prerogative. But if somebody wants to probe it, a friend of Comey (Mueller) has a conflict. Is Mueller trying to taint his case? Finally, Sessions isn't recused from this "obstruction" nonsense, any more than he was forbidden from recommending Comey be fired. Has nothing to do with the campaign, and everything to do with how Comey conducted himself.
Sessions is not recused from investigating and prosecuting Manafort, Gates, or the 13 Russian trolls. Mueller got those cases by usurping Sessions' authority - taking cases that Sessions is not recused from - and Mueller ought to know what Sessions is recused from.
The people perpetrating this problem are Mueller and his boss, Rosenstein. By protocol, Sessions can't just butt in, the system is presumed to be run with honest and reasonably competent operators.
This judge just threw a big monkey wrench into Mueller's plans.
Sessions is AG and is responsible for everything in the department. It is even his prerogative to change his mind on anything in the performance of his responsibilities.
Remember: Sessions declared that the special council should "conclude" its work. That is most demonstratively a 'butt in' - if you will.
Sessions may be 'out of the loop' on the decision making but he is not out of the responsibility loop of departmental outcomes.
Like it or not, Sessions is the AG and whatever has gone on at the DOJ after he took his oath of office is his responsibility.