PvP - Charging up the charged attack

There doesn't seem to be such a thing as too much tapping in my experience. I've found the two finger tap (alternating between fingers) or using twitch muscles to tap the screen at a rapidly fast pace both work well for charging up moves.

Fast and constant is needed to get a full charge. Tapping inside the circle is not necessary. I can tap fastest using my wrist and index finger to get to the max of 3 rings.

I’m not a fan of the tapping. I wish instead that they used the pokeball throwing mechanic. Essentially, the smaller circle you hit, the more damage done.

I believe it is more dependent on where the tap is at the end of the timer, and I think you can actually get tired even tho it is only 4 seconds.
I have heard people have had success "finger tapping" with 4 fingers. I have had mixed results with that method. I have had much better results with a 2 finger tap. My index and middle finger hitting at slightly different times. Keep your fingers close to the screen. The motion seems closer to a rub than a tap. Not to be graphic, but when I was showing an explaining it to my wife, she smirked because it was like I was explaining how to rub a woman, if you know what I mean...

As soon as you hit the button, brace your phone as best you can and then tap like crazy with your index finger in the center of the circle. Wait for it to zoom in. Tada.

Venusaur got 2 quick moves razor leaf and vine whip
u should use vine whip pared with frenzy plant it gains much faster energy