The Steelers would only save about $250k against the cap if Holba makes the team over Warren.
I am not defending selecting this long snapper or any long snapper (when you still have one who did a capable job last season), but I understand doing it in the 6th round, instead of waiting until their pick in the 7th, if they felt he was the best LS and felt he was going to be drafted. Essentially, because they picked so late in the 7th, the Steelers had no shot of drafting Holba, if they thought he was going to be drafted, unless they took him in the 6th. 6th and 7th round draft picks have essentially zero difference in the likelihood of ending up successful pros, so there is very little practical difference between the picks and when a team is picking so late in the 7th, they basically have to use their 6th to take their last player they want, who they project to be drafted. After that, you just use the 7th on the last lottery pick you think has a shot or might be hard to sign as a UDFA.
Think of it this way: If the Steelers took Adams in the 6th and Holba in the 7th, would anyone really have an issue with it?