I actually don't buy in to the narrative that he played awful, boring football. Sure, we didn't fly at teams like big Ange does at Tottenham but it was hardly Simeone. I'd say style wise it was middle of the road and reasonably well balanced.
My big issues with Southgate are that he himself is boring, and his him game management is poor. I feel like in International football you can cope with being a mood hoover because you can go weeks / months without being heard from, and the players have minimal interaction. I think in club football it would get old very, very quickly.
Summary - Nice guy, steady guy, nice human, good with the media, boring and dreadful in game decisions.
It's a hard pass for me as Utd manager but I think he's decent for international.