Grass is always greener on the other side of the fence, isn't it? When we got Kolasinac most were raving about him and especially opposition fans were incredibly jealous, everybody thought he was the best LB in Bundesliga just the season before. And now we are asking for a 21-year-old, that back then was 19 or so, and still hasn't produced anything near the best of Kolasinac (which was in Germany.) At the same time, we are slating a lot our projects (academy products or otherwise) as not good enough, just as we are slating Wenger's youth policy in his later years, that indeed produced very little. It was obviously just our scouting network to blame until now and the keyboard scouters need to be listened to regarding Chilwell, he will instantly improve us unlike Guendouzi, Holding, Chambers, Bellerin, Coquelin, Iwobi, AMN, etc.
Kolasinac hasn't had the runs of games a player needs to really establish themselves at a big club, plus the formations have changed a fair bit. He's still fairly young, it would be reasonable to wait to see him play LB for a good run of games in Emery's system before judging what he can really offer.
My problem with him is just that I think he'll get a lot of injuries in his career. What other elite footballer is built like him? I can't think of many. Plus to be an elite fullback these days you need immense stamina and fitness. I just think the sheer size of him is always gonna cause problems with injuries. Bellerin has the ideal build for a fullback.