There was no huge gap between (I think Atherton is of a similar view).
Russell's work was frequently untidy and his drops/misses glossed over.
Stewart success rate on catches was pretty high but every drop was blown out of proportion.
I recall in a Test in the Windies the pitch was rather two paced, and the bounce was erratic. Russell stood further back to the likes or Frasier than the home keeper did to Ambrose and Walsh because (he admitted) he was worried about being hit. In consequence several edges fell short of him (and the slips who, rightly, took their mark from him). I have no doubt the Stewart would have moved up, risked being hit and not being able to handle one or two deliveries that really flew, and created many more chances for himself and the slips.
Stewart - badly underated as a keeper.