I don't put Drinkwater who's older than both by a bit under same umbrella as Oxlade and Barkley. There's a clear difference between the former and the latter. Drinkwater never had a high ceiling and won't improve as a player - he's set. Oxlade and Barkley still have untapped potential and have shown flashes of high level ability. They are two of the better English talent out there. The only ones that are better than them are the Spurs lot (-Dier), Rashford, Sterling. They can still improve as players - they aren't "set". We're an English club so we need some good English talent. Maybe they aren't the best but they are at least Chelsea acceptable level. They'll be part of a strong squad in the future.
Aurier is only going on the cheap because PSG desperately need to sell and he isn't a main 11 player - if he was starting there he'd be costing Spurs £50m imo. It doesn't quite work like that. Barkley at £25m isn't too expensive. Oxlade at £35m - a bit overpriced but Wenger really didn't want to sell so put up an overpriced tag. Drinkwater I've already said a lot on before, don't think he's a good buy - he is not needed if we're signing two English players as well.
Honestly, for English talent? They're both good players with some interesting qualities. Barkley in particular still hasn't got a set position at all - Conte gets a blank canvas to work with. Both good signings in a crazy market.