Poole and Glow aren't really the same 'type' of OG.
It's pretty clear based on the picks and projects/FAs we're signed, that Cable has two prototypes for each OG set. This roster is now littered with them. At LG, we've opted for size (~320) while at RG, we've preferred guys right in the 295-310 range. Crazy movement skills have been a premium there with all but Moffitt having really good agility.
While Seattle is light on immediate quality to replace Okung, it's certainly not been for a lack of effort. Garrett Scott was about as close of a prototype we've chosen and it was a real shame that his heart defect robbed him of opportunity. But even now with Gilliam and now Davis, we currently have 2 mirrors for Okung physically. Getting LTs that fit our physical profile is not very easy. This is a big year for Gilliam.
Glowinski, from the moment he was chosen, struck me as an obvious successor to Sweezy. I fully expect us to want to resign him, but for him to get priced off our roster on the open market just as Tate was. Glowinski appears in every respect to be a very strong hedge against what I assume, and what Seattle presumes, will be a tough player to retain. Everything about him, and how he's being groomed has confirmed that speculation in my view.
I'm actually quite encouraged by the 4 new OL we've added. And I would not be the least surprised if 3 of them made the opening day active roster. It's worth noting, that while Gilliam is a relative unknown quantity, he was good enough even in his first year in transition from TE to OT, that he made the active 45 in all but one game last year. Pete clearly has a lot of regard for him, because he's not shy about leaving players off the list if they aren't likely to be tested.
I would say that Gilliam's progress is worth watching the closest this year amongst the OL group. Because if he develops and continues to earn the coach's confidence he's probably our 2016 starting LT. If Seattle manages to groom and develop a LT from scratch in that fashion -- that'd be a huge win for the club in it's efforts to keeping the roster at a high level. Poole, Glow and Sokoli probably will have significant growing pains as this is their first year. Pains that could be masked if the starters remain healthy. Gilliam is in year two and should be at a point where he starts being effective on the field.