19-20 year olds Martial and Coman were the only alternatives France had in the '16 final. Not starting those two was a logical decision. England's attacking depth is far stronger than France had that year. For the sake of argument let's assume France (based on the '18 final) would have dropped one of Mount/Foden/Grealish for Henderson. You get more defensive cover but that's still an XI with proper intent.
Portugal are pragmatic yes, that's why I didn't mention them. Spain however would definitely make the most of this English generation. They were also stacked with options between '08-12. Imagine if they had a cautious and safety first manager, their equivalent would have been dropping one of Xavi/Iniesta for an extra defender like Arbeloa/Albiol.
When you've got the likes of Foden, Mount, Sancho, Grealish, Kane, Rashford, Sterling at your disposal it's borderline criminal to use a formation with 5 defenders and 2 defensive minded mids like Rice and Henderson. With Kane being nailed on that leaves two spots for six highly talented players. That's a huge waste of talent.
I would sort of understand 5 atb if TAA was RWB with Rice+Mount in CM. The extra CB would cover for TAA being hyper-offensive plus any deficiencies Mount has in a midfield two. But TAA looks highly unlikely to start and the CM will most likely be Rice+Henderson. Soutgate's team will probably be close to:
Pickford
Walker - Stones - Maguire
Trippier - Rice - Henderson - Chilwell
Sterling - Kane - Grealish
This is plucky underdog territory where the main objective is safety first. A rather underwhelming team and a huge waste of potential imo.