Well, Giannelli sets up fast and the height overcomes the need for jump sets. It's true Russell and Kovacevic are fast OHs but they don't require a fast ball in front or the need for an even lethal opposite should've been of higher priority for Trentino than another high ball attacking OH which they desperately needed last season . They probably need most of that speedier setting from the backrow though as both players are trained to kill BIC sets than pipes but in front. I just have to disagree with your post.
As to attacking ability, I make two categories for OHs.
One category is the "strong" OH like Leon, Kliuka or NGapeth. They can score even with a poor set up, or facing double or triple blocking. They have to deal with most difficult balls.
Another category is the "technique" OH who replies on system and fast setting. They have trouble to do the same spikes as strong OHs do. Both Aaron and Uros are "technique" OH in my opinion. Sure, they can still finish difficult balls once in a while, but their attacking relies on fast set up more than strong OHs do. If a tech OH plays like a strong OH, their attacking efficiency will drop for sure, averagely.