There are pro’s and cons to walk both ,the coastal or the central.
one loves pudding ,the other loves yoghurt. One loves the daughter, the other one loves the mother. There are others who love both.
I agree with your point about historic places but that counts as far as Baiona because places like Pontevedra and those on the Variante Espiritual share the route with the central route.
if you ask any Portuguese to mention the most interesting and historical places in the northern districts Viana do Costelo and Minho , first is Ponte de Lima , second is Barcelos and third is Valença do Minho. All are situated along the central route .
And if you take a day off in Barcelos within one our hour by bus or train you can visit the wonderfull and beautiful ancient Roman town Braga , with the world famous sanctuary Bom Jesus do Monte , mentioned in all lists of World Heritage sites .
we stayed two days in Barcelos to enjoy that medieval town and as a bonus went to Braga.
Every year I come to Portugal I go to Braga . It makes me happy to be there.
And yes here and there you walk alongside roads, you share with traffic.
the busiests roads are when you leave Porto .So most of the hikers walk from Porto along the Douro river and Atlantic coast to Vila do Conde with scenic sea views but if you are there during weekend you have to take care for recreative hikers and bikers on the long and very small boardwalks, approaching you from behind and towards .They claim their presence too so unfortunately you have to be very carefull for your own safety
and yes you share a short busy track with the traffic nearby Pedra Furada direction Barcelos for about one kilometer but there are places ( e.g. from A Guarda to Baiona on the coastal where you wallk on the hard shoulder of a national road for miles.
and if you walk the original coastal ( Senda Litoral or Beira Mar) you have to be lucky that the weather is good. We once faced heavy rains and strong winds during 4 or 5 days . Then it will be raining too more inland where the central is and you get wet too but it will be better to stand because of less seawind.
Once we stayed around Viana do Castelo with our caravan and had 10 days of heavy rain so left the caravan there on a campingsite in Vila Praia de Âncora and waited for better times and made daytrips all around the north of Portugal.
I hiked both routes several times and I liked both and walked both in their original forms and also mixed both.
that is the charm of the Portuguese route in Portugal.you won’t find this on other caminos to Santiago.
once in Spain the arguments do not count.
Baiona is a historical place but after that you walk into Vigo, one of the big cities to walk through In Spain. Chaotic, stinking exhaust damps of cars and heavy traffic , lots of roadworks and diversions ( I was there a month ago
)
so my two cents are walk out of Porto along the river and the coast to Vila do Conde
and from there head inland to the Central (São Pedro de Rates ,Barcelos ( sidestep to Braga) Ponte de Lima and Valença into Spain where the first town you meet is the characteristic medieval town of Tui and join from Redondela with them who came from the Coastal route and share your experiences and get infected by the Caminho virus which means that you want to come back next year and then walk the route you haven’t seen yet,.
i do this since 2013 every year and mixed all possibilities.And there are lots of it.
And my higlight every year again is to stay at the best albergue of the entire Portuguese caminho ,
casa da Fernanda . Don’t want to miss that. I must be there every time again when I am in Portugal