I think the format plays a huge factor too but for different reasons. This format of racing is very dependent on aerodynamic advantages - to the point that even on the massive climbs the rider on the wheel still holds the edge to someone doing the work. On the flat stages the peloton is almost always going to catch a breakaway. Any marginal advantage is super useful in that context and the well funded teams push to optimize everything. I think it’s more likely than not there is cheating. Motors seem unlikely but with this kind of money and international attention marginal advantages like microdosing for example will be exploited. People cheat in everything and often get rewarded for it. It’s an infuriating fact of life.