I agree about Arguello. He's the one of the young Argentine group to watch. I also like Andreozzi and Pella, and DelBo may not belong with this group but he's still young. Arguello has the biggest game of the young Argentines.
Velotti has hype for beating fellow 15-18 year old kids but out steadying them and having good feel for his shots. This is the big leagues and as you said, his game isn't big enough. That backhand of his is awkward, especially the slice he hits. He lacks a kill shot. And I think his footwork is mediocre. We'll see how he improves with more experience.
Yes, why not Pella, he's having the most success right now.
Forgot Bagnis too.