have observed that the spool up time required for takeoff is significant
Much depends on pilot technique. Take off procedure in the 737 includes firstly opening the thrust levers to approximately 40% N1 to ensure spool up is equal. The FCTM recommend no longer than two seconds after the N1 reaches 40% then select TOGA. Otherwise the take off performance is compromised.
Is it possible you are mistaking the hesitation at 40% N1 as part of the total spool up time when it has got nothing to do with it?
My recollection is that from idle of 23% N1 to 40% N1 there is up to three seconds tolerance between any engine in rate of spool up with equal thrust lever angle. However, from 40% N1 to take off power using autothrottle the tolerance between engines is only one second assuming both thrust levers advance equally.
The reason for the 40% N1 figure is that if TOGA was used from idle of 23% N1 and one engine took the full three seconds of allowable tolerance, while the other engine accelerated normally to high thrust, the aircraft would likely become uncontrollable in a very short time and in danger of leaving the runway centreline at a high angle.