I don't think you'll be proven wrong Monday, or at any point this year. I think the defense will be pretty ragged this season, unless a really good pass rush and a 3 tech emerge.
As for the defense in the first preseason game, I disliked some of the alignments. A few times outside corners were 10+ yards off the line of scrimmage, which I hate. I hope we don't see much more of that, especially outside of 3rd and long. But the players in the secondary won't get many chances to make plays unless the front can get stops on early downs and get pressure in passing situations.
I don't have a problem with the scheme. It's not my favorite; I'd prefer a man based coverage philosophy, but zone has it's advantages. On the field, it's more effective at defending mobile QBs; for team building, it's less expensive. The key -- as it is with almost everything -- will be good drafting and good player development. Find good players, and help them succeed. If they don't do one or both of those well, it doesn't matter what scheme they run. But I don't think the scheme itself is flawed. It's had plenty of success, even in the modern NFL.
It is way too early to judge how any team is going to do with only 1 pre-season and a few practices under their belts.
What the coaches are looking at are bubble players and different lineups at this point.
We can all have our different opinions but till the season starts we just never know.