To be fair football changed a lot since the Fergie days. Even if the player is British who is to say he won't move away ? Bale rejected us for Real and was not feeling like coming in the past. De Gea has been our best player and I'd rather take 5-6 years of a world class player than 10 years of beans, beans, beans.
No one is arguing AWB and Maguire would better us, however they come at premium price and who is to say they are better than continental options? You can see teams like Spurs, Liverpool, City, Chelsea who are more consistent these days going for continental players rather than your British core. Even Leicester go for continental players these days. Wolves who were a very good side also last year rely on Neves, Jota, Patricio, Jimenez, Moutinho, Boly. I struggle to name a team that had a successful spell bringing young British core since Fergie years.
Forget British core but clubs which dominate usually have local core. There are exceptions like City who struggle to fill their HG quota.
Chelsea reached CL finals twice and they had 4 English players in first 11 (with Terry suspended for second finals).
When ManUtd reached 3 finals in 4 years they had 5-6 British players. In 2008 we had 6 in starting 11 and 2 on the bench.
In 2018, Liverpool had 4 British players in the starting 11.
In 2019, Liverpool had 3 British players in starting 11 and 2 came on as a sub.
In 2019, Spurs had 5 British players.
So any time English team reached CL finals, they had good enough British core players. Obviously it's always the balance. You have to balance this with very good foreign players and having British players for the sake of it won't work either.
Coming to the local core. If you see any team that's dominating their leagues and CL, they have local core.
2017 and 2018: Madrid had 3 Spanish players in the 11 and 2 came on
2017: Juventus had 4 Italian players and 1 came on as a sub
2016: Madrid had 2 Spanish players in 11, 7 in match day 18 squad. Atletico Madrid had 5 in the 11.
2015: Barca had 4 Spanish players in the 11 and 2 came on as a sub. Juventus had 5 Italians in the 11.
2014: Madrid had 3 Spanish players in the 11 and 2 came on. Total they had 8/18 in match day squad. Atletico had 6 in their staring 11 and 1 came on as a sub
2012: Dortmund had 7 German players in their 11 and 1 came on. Total they had 11/18 German players. Bayern had 5 German players in their 11 and 1 came on.
2011: Bayern had 8 German players in their 11 and 2 as subs. Chelsea had 4 English players in their 11 and this is with Terry's suspension.
Key is to find the balance. Sign the best possible local players or best possible young players and then foreign players.