Yes, your Giant's pedal assist system is from Yamaha (with Giant's specific tuning. Kind of like what Specialized does with the Brose system on their Vados, Comos, etc.) The Yamaha systems are very highly regarded in the e-bike world for their smoothness and reliability.
Of course the Bosch is no slouch either, and likely commands the top spot (in number of units in service) of all e-bike mid-drive systems. But like you, I feel that the Purion display leaves a lot to be desired.
I can't tell from your above post whether you are going to keep or return the Trek? If you are going to keep it, understand that you can replace the Purion display with an Intuvia if so desired. Comes at a price, but worth it in my opinion for the extra data the Intuvia provides.
Finally, don't confuse 'power' with 'speed' on e-bike assist systems. For power (which is generally the more important number for us), look for the torque specifications (listed in Nm units). If you look at similar motors from, say, Bosch, you will many times find that the 'speed' version (class 3, 28mph assist) has a lower torque rating as compared to the 'standard' (class 1, 20mph assist) motors. Torque is what helps you climb the hills more easily, although you may then be limited by the system's top pedal assist speed.
I recently purchased a Haibike Trekking 7.0 with the Bosch Performance CX motor. It is a class 1 bike, but that motor puts out 75Nm of torque up to a pedal assist of 20mph. The higher spec Trekking 9.0 S is a class 3 bike with a pedal assist up to 28mph, but its torque output is only 65Nm.
At the sake of potentially invalidating my warranty (and lowering my bike's range per battery charge), I am going to add a tuning chip to my Performance CX motor, which will delete the 20mph assist cut-off, while still giving me the extra power (torque) of the CX motor. Best of both worlds? We will see. But I have other class 3 bikes and am somewhat addicted to their speed. I refer to it as 'e-bike crack.'
