Losing a single match in the Premier League when you are leading the table can drop a team to the fourth because if you look at the top three in the Premier League table right now, you will see that the point difference between the first position and the second and third is just one point, while the points difference between the third and the fifth is just two points; this is indirectly telling you that If Manchester City lose one match, they can drop to the fifth place.
Tottenham have a very good start, they still have chance to compete for the title because they have good players, and their performance against big teams is not that bad, just that red card and injuries affected them.
This is what makes Premier League is the most exciting league in the world. Teams who wants to challenge for the title need to prepare in every aspect required for a long competition with many competitors who have same level of quality. A quality Squad Depth is one key for a team to win the league. Tottenham dont have this factor. when they lost their important players, their form drop instantly. with this situation they have, I dont think Tottenham will stay competing for the title. finishing top 4 is an achievement for them.
Yes squads depth is definitely the key to win the league. Without squad depth definitely run is gonna be a short one as the team can get into trouble if you are hit by injuries. Spurs do lack in some areas but the good thing is that their injured players will be back in January so not a big worry. Long term injuries would have affected them drastically though. The only thing they need to do is do their best until their players gets recovered.