Good call about Diomande but it's too soon for him. I firmly believe that he will become one of the best CB in the world. He needs at least two more seasons at Sporting. His physical attributes are incredible, his quickness, aerial presence, he got the full package for the Premier League.
He just needs to evolve a bit in technical terms, work on his concentration lapses and gain experience.
I think Arsenal has him shortlisted already. He will definitely end up in the Premier League in the future.
I really like Diomande and I also agree that staying at SCP for a few more years would be great for his development. But think if he can kick on from last season and improve a little bit more, then I think some club will make a serious attempt to sign him. At 19 years of age, he's showing big potential for a RCB.
Regarding Todibo, he was at Toulouse before he joined Barcelona at 19. He rejected quite a few big offers from clubs like Man City to join Barcelona. But I'm not sure exactly what happened at Barcelona, but at his young age, he needed games for his development and he then was sent on loan to a club managed by Jorge Jesus. And it seems like he now has stability at Nice, as far as playing games is concerned, and he's showing his potential. The mistake I feel he made, was not joining a top 4 French club after leaving Toulouse. I think if he had joined a Monaco or a Lens, his development would've been more stable.