Royal actually had a good game last night so it's such a weird time to pull this one out of the bag again, what do you want from this discussion, do you need everyone to agree with you? It's clear you want Spence to play and every Spurs fan wants all Spurs player's to do well in our shirt and Conte is currently the man who picks the team. Your idea of how well Spence would do is based on a different level of understanding as the coaching staff, that's true for every fan, I really want him on the pitch too.
To attempt to answer your hypothetical question, I think you know it's about how a defense works as a unit rather than individuals, whether it's a back 4 or 5 (3 cbs with 2 WBs) as well as it being dependant on the opposition we are facing - So for last night, Royal is on the list for me but it depends on the moving scales involved. Romero is probably the only absolutely indisputable shout consistently but any of those who have played could be.