What graph are you talking about in the non premium Strava account? The speed graph?
Power spikes are normal. Using a PM is helpful to smooth out your application of power. You’ll get better at it, which will make you more efficient. As an aside, the best way to do that is to take it off 3 second average and go with real time power.
How come your not referencing the power analysis in the Elemnt Bolt app? It’s light years better than Strava.