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.
Yes, it cannot be denied that the EPL is the league with the tightest competition and the most competitors from top big clubs. So, every club is obliged to perform well and excel in whatever conditions. However, on the other hand, injuries to first line players at a religious club is a challenge in itself. For this reason, the coach must have the ability to change strategies as best as possible in times of urgency and choose the most suitable replacement. Even though they may not be as strong as the first line players, at least the club will not be so devastated when a main player is injured.
Regarding Tottenham, and other clubs too, when a player has just been injured, especially a fairly serious and long injury, of course this will not be good. Because after all, usually after injury, the performance may not be as good and strong as before. So there may have to be a little more adjustment, unless it's not a major or vital injury.