I think the route markings are 10X better than the dots as it shows intent. With the dots, you have to guess the intent. For example, the point of the mystery Oregon SC southeast of Woodburn would become clear. I agree a combination of both would be good.
Also, on the route markings, I think it's safe to assume that there won't be SCs at the end point. So Cardiff probably would not get an SC.
Maybe on the longer routes the intent is clear, but my point was that on these shorter routes (where you can travel the entire route on one charge) the intent isn't clear at all.
For example, did they draw the line to Cardiff because the intent is to support driving to Cardiff and points beyond into South Wales? If so, a good place for the Supercharger would be around Newport (140 miles from central London, and within a single charge of pretty much anywhere in south-east England (Canterbury 208, Ipswich 226, Cambridge 190, even Norwich 258): if the intent is to feed South Wales, there's no point placing it further east. On the other hand, putting it there is useless for reaching the South West (there's the Severn estuary and its toll bridge in the way), so a charger around Bristol would be much better, serving both routes. Or a third interpretation, to optimally serve round-trips just on the route shown, maybe you put it slap in the middle of the blue line at a service area near Swindon. This would still just about serve those two routes from London, (Swindon->Penzance 228 miles, further than from Bristol but still OK) but not useful for those starting from Birmingham or points north.
Maybe the problem isn't the concept of route lines, just lack of care in the application - if they'd drawn a Y-shape splitting at Bristol, then I'd have less to complain about. But on the whole, dots would make it much easier to work out whether the routes I care about are covered or not.
[fair disclosure: I often go on holiday to Devon/Cornwall by car. But when going to Cardiff, I almost always take the train].
