I find poncho's are ineffective without rain pants. The rain tends to wick down your legs and into your boots.
I did wear a rain jacket last year during the one storm and found I became more wet from perspiration that rain. I would have been better off with rain pants and tee shirt, just letting the Tee get wet.
A poncho is a single use item. It is only good for rain. A rain jacket and rain pants double as insulators. I don't carry long underwear and one less layer on top. If I get cold I don my rain gear.
So in the end I recommend rain jacket and pants and no poncho. BTW I just returned from an 11 day trek with the Boy Scouts in Philmont Scout Ranch in New Mexico. We were rained on 6 of the 11 days there. Both heavy rain and hail. The Boy Scouts recommended rain jacket and pants not a poncho, worked well.
Buen Camino