Barlow is extremely good at pressing and borderline elite at winning arial duals. He's also good at winning races to balls. This makes him useful in the later stages of a game where you're protecting a lead or draw. He helps keep the ball in the opposing end, wins headers in midfield, and is a top defensive marker in the box on corner kicks and free kicks. If you're trying to get out of the final dozen minutes without conceding a goal, he's probably one of the best players for the job in all of MLS, honestly.
Does that make him useful beyond limited situations? No. Is he overused? Yes. Do I wish we'd sign a player who could do those things but also not completely fuck everything up with the ball at his feet in the final third? Yes. Does he still more use than any of the guys you cited have shown the last few years? Yes. Would those players perform even worse in a pressing system? Probably.
The baseline for Mathis was starter for a mid-table Bundesliga team. He was reduced to a decent MLS player. That's an absolutely massive dropoff. The equivalent dropoff for an MLS All-Star would render them less than MLS quality, to say the least. Age has nothing to do with it. Players decline differently. Zlatan is still a top player at age 40 while Wayne Rooney was basically done in his early 30s. You're citing players who have absolutely sucked the last couple of seasons.
its funny that your saying they suck the past couple of seasons because they were hurt.
under your logic, players like long, Morris, hyndman are also terrible because they didn't play last year. injuries happen and it takes time and commitment from the team to get these players back to form. i would argue that the teams dwyer and agudelo played for did not have their interest at heart. life is not as simple as you say. the players i mentioned are not that old and can still revive their careers if they are willing to press. we already saw how much gam is being thrown around. you revive the career of one of these guys who are on a cheap contract and you can get some serious allocation money. this is where you can buy low and sell high.
to keep barlow because he is a great at pressing is just not good enough. if the team wants to keep him, send him to rb2 to help build a culture for that team but he is not an MLS player.