Your shunt configuration is wrong, actually. A shunt field is powered continuously, from a separate source from the armature.
Series was fine.
It's all about how the magnetic field for the armature is created.
For larger motors, a series field and a shunt field are wound very much differently.
In Series, the field winding has to be able to handle full armature current. A Shunt Field is typically much smaller wire, with many more turns. Series Field motors were most often used as traction motors, as the field coil would develop a very strong field at zero speed, with a huge amount of current, but would eventually moderate the field strength as the motor speed (and back EMF) increased. A series field motor can generate a LOT of torque at standstill. The ability to weaken the field in a controlled manner really doesn't exist, but could be done in a limited (and expensive) fashion with different field taps.
The Shunt Field motor has a relatively low field current, but again, with so many windings, it doesn't need to be very high current wise, and the field strength remains constant (more in a minute) no matter what the armature load is. They don't have the standstill pullout torque of a series field machine, so many larger shunt wound motors had an internal, smaller (magnetically) series field, to provide boost torque at low speeds. These worked fine, for many applications, but not all, as reversing the motor is an issue. Swapping the armature polarity would result in the series field partially cancelling out the shunt field. So did reversing the shunt field partially cancel out the series field.
In most cases, for modern (newer than 30 to 50 year old) DC Machines, it is generally just an armature and a shunt field, which can still deliver full rated torque down at standstill.
A shunt field, also allows for an easy method of running above the base full speed of the motor by reducing the field current. Base speed is the point where the motor essentially switches over from a constant torque machine to a constant (horse)power machine.
Two things to never do with a DC Motor: Never run unloaded with zero field. Residual magnetism can make it accelerate destructively, and Never just disconnect the wires on an energized shunt field. The resulting arc is Very Impressive, due to the stored energy in the field.