This is a complicated thing to answer clearly, one thing being we have little records of the reasons of why a city had been founded where it was, and the other more important one, being that of course geography, climate, meteorology, hydrology and a bunch of other environmental conditions - both global and local - had an effect, and it's really hard to measure what was the main.

Now, I am really struggling to understand what would be the supposed decisive effect of the Coriolis effect for the location of the cities on what you term "right bank" of rivers and river mouths. Especially on the global "North hemisphere" scale where I can easily find examples to the contrary. But let's limit the scope to just Portugal - which is the area you mentioned as first, and which happens to be the subject of my flair. Now first thing to point out is that Portugal ( apart maybe the Algarve region) is a relatively homogeneous geographically - in admittedly very broadly and vaguely defined main features. It faces the Atlantic coast, it has a pretty straight North-South span, with most, if not all, of the rivers are flowing in an East-West direction and entering the Atlantic. It shouldn't be really surprising that multiple cities and locations in this area would have similar features, as it would be incorrect to generalize from this region to other places which don't share similar features, like the entirety of hemisphere, or even the east Iberian coast.

Now, for the Coriolis effect on Portugal and the position of it's cities and harbors, it might even have an effect, albeit indirect. As far as I am aware, Coriolis effect is part of the reason why the Gulf Stream has the flow it has (in the NE direction from Americas to Europe). In the vicinity of Iberian coast the Gulf stream turns southwards, and the predominant current on the West coast of Iberia - which includes Portugal, is in the Southern direction. For ships anchoring in a bay or river mouth where such a current could be felt it would generally speaking be safer to anchor near the northern bank where the coast would shelter from this current, and dangerous to anchor near the southern bank as the current might throw the ships on the coast! In Portugal's river system, the "right bank" would be the northern, and as such safer, and "left bank" would be southern and as such in average more dangerous. But I just want to make this crystal clear: this is a generalized overview and the exact micro-location's geographical and topological features would make more importance than pinning everything on Coriolis effect. More so, as the harbors in question were all some way inland from the coast, it's a question how much was the southern current effect even felt. It is possible it wasn't even a factor.

And you could notice that at this point we aren't even talking right bank-left bank, but northern-southern bank and as such has little to do with Coriolis. In deciding a town's location, anotherr feature for which northern position might be important exists. It is the amount of sunlight an area receives, an important factor for agriculture which for a town, whether just founded or well established, is very important. In the northern hemisphere, the river bank's the northern side directly faces the Sun over the tropics and receives more direct sunlight then the southern side which could be in shade, especially if there are slopes and hills involved - like they are in Porto for example. Again, micro location's features like hills, slopes, relief, and the ground composition are probably more important factor here. But you will find time and time again best agriculture position - for things like wine at least. - being on slopes on northern banks / coasts, facing South and directly exposed to the sunlight. The town being on the same bank would allow easier access to such locations and as such be a advantage. Not to mention the city itself would receive more natural light.

To sum up. Many things were a factor for where the cities were founded. Coriolis effect could in an indirect way through the Gulf Stream be one of such factors for the Western Iberian coast including Portugal. Was it the most important? Most likely not.