It does seem that things are close. What bike is fastest seems to be decided by the type of event you ride and therefore hydration / nutrition needs.
Short TT’s + some short tri’s (typical UK time trial scene non UCI) with no bottles or hydration required. No need for integrated storage or hydration, possible single ring set up so removable front hanger good.
UCI style TT - UCI legal set-up one frame mounted UCI aceptable bottle (depending on distance/hear etc). Probably 2x gearing as courses often more sporting than a UK drag strip course.
Olympic Tri and 50mile TT
Not UCI legal - one or two bottles worth of fluid and a storage for a few gels & maybe flat kit.
70.3/IM’s/100mile TT’s
Non UCI - Hydration 2 + bottles worth of fluid, ability to store handed up standard bottles or pour fluid into hydration storage, nutrition gels/food storage + flat kit storage.