I think they see Barnes as a Sam and will probably run a lot of 5-2 this year. I think they'll look for a hybrid safety\linebacker later in the draft for use in the nickel.
What you are missing is that your conclusions are not based on facts, he doesn't have a lot of swing and miss, he has a relatively low k rate and he makes a lot of hard contact, he has superior strike zone judgement and he has been very young for his competition level. He also should end up as a plus defender.
It's not just to stop the run, though. In this era of mobile, escapable quarterbacks, they want ends that can control the lanes and gaps and crush and contain the pocket.
Where did anyone get the idea Hassanein won't be strong against the run? He's raw in every aspect, but stout enough, strong enough and motivated enough to develop.
They picked late in the draft and ended up with three starters in their rookie years. If they got a starter in Teslaa with a late 3rd and two picks after the 3rd round that is a steal. If any of the other picks end up helping at all, that's a bonus.
Last year wasn't so bad, Reed much better before he got hurt, Lopez, Ya-Sin, Maddox, Allen, Stewart all pretty solid, got some immediate help and at least 3 solid starters out of the draft, not all bad for tight budget and drafting late.
If Clark goes 6 for 20 and catches every ball, he's still the same player, with the same abilities, at the same level of development, and he'd be in the exact same situation. The coaches understand this and are not basing their judgements on superficial stats.
Same with McGonigle, if he was hitting a buck fifty, but showing the same abilities and development, he'd be in the same position.
Talent matters, ability matters, developmental progress matters, performance matters. Spring training stats don't matter. Can they be an indicator? Sure, but small samples are notoriously unreliable, especially in an uneven environment like spring training.
Do you think you are making some point? Valencia hit .353 and got sent back. Clark wasn't making the team no matter what he hit. They want the younger guys playing full time in minor league camp, and there isn't enough playing time anymore for the younger guys in the big camp as they ramp up for opening day. You can't read any more into it than that.
He's slow, isn't shifty or elusive, his instincts aren't great and he's dinged up. Whatever reps the #2 back gets, I'd like them to be more of a threat.
Of course players are competing for spots, that was never the point. The point is small samples of stats in spring training are not a reliable indicator of ability or competitive status, and fans grant them way too much importance.
It has nothing to do with "riding the hot hand", it's the exact same sweet swinging Kevin McGonigle, but facing different pitchers and circumstances and randomness that produces very different results in small samples. Baseball is a frustrating game where you can do everything right and still get negative results over the short term.
Hypothetical for you. You clone Kevin McGonicle. Exact same player in every way, and alternate them through the first ten games of spring training. One goes 1 for twenty and makes several errors in the field, and the other goes 10 for 20 and is flawless at short. Which one goes north and which one to AAA?
You can be the exact same talent and go 1 for 20 or 10 for 20, proves nothing, especially early in the spring. Coaches know who has ability despite the stats, fans have only stats to go by and so assign them way too much importance.