The right back issue will be hotly debated over the coming weeks precisely because it is worthy of debate. It's not like we have a choice between TAA and say, Stuart Parnaby. Our right back options play for the teams in 1st, 2nd, 4th and 5th in the Premier League and the side currently top of La Liga. I would take TAA for his ability on the ball, but I would have big reservations about him defensively against the likes of France, Germany and the Netherlands. I've never particularly likes Kyle Walker, but he could (like TAA previously) win a Champions League later this month and has multiple PL titles. Reece James could also win the CL. Meanwhile Trippier, who has never let Southgate down, is on the verge of winning La Liga. Wan Bissaka doesn't even enter most people's calculations, but he is arguably the best of all at actually defending.
As stated, I would take TAA personally as his form has picked up massively in the past 6 weeks or so. I'd also take Walker and Trippier in a squad of 26, given these two can cover for CB and LB. But Southgate can't take everyone and should he decide to take only 2 RBs and leave TAA at home, I won't be calling him clueless as a result.
As for the OP mentioning Sancho, was there ever any doubt that he would make the squad but for injury? He's far and away our best right winger and one of the most accomplished 21 year olds in world football.