Bergvall is a very different midfielder to Devine in being a 'flair'/creative player and although its early days likely to be an 8/10 hybrid more in the mould of Maddison or Kulusevski or even a Bentancur when he is playing more forward. At the moment I think Bergvall is finding PL players think and move more quickly than he has been used to in Sweden and he is being caught out by that. I'm sure he's adapting, but it might be next season before we see him having adjusted and he'll then look a good player - how good we'll need to wait and see as even next season at aged 19 we will not see the finished player.
Devine is much more of a 'gritty' player who can certainly play as a no 8/10 with excellent short and long passing which can create chances, but he's also able to drop back into a 'deep lying' creative player' /no 6 role perhaps closest player I can think of being a Michael Carrick but slightly less finesse and more able to look after himself if necessary (eg Devine as a 16 year old making his u21 debut, Chelsea's England midfielder Danny Drinkwater then in his mid 20's decided to 'take liberties' with Devine. After a 2nd incident, Drinkwater was howling on the ground ...... I think Devine's rugby league playing father had taught him some of the 'black arts'). Devine looked very capable last preseason and I think it was 50/50 whether he stayed at Spurs or had another loan to get more first team experience at Westerlo : I think Devine will be a useful addition to first team next season (or even January) categorised as a List B u21 so increasing the size of the squad, rather than taking up a squad place.