I think it depends on what type of elements you ride in and how exposed your cables are. I've had standard bulk box type cables and housing work perfectly fine for me for thousands of miles on my TT bike that didn't usually get used in the rain, and the cables are internally routed. But for my old CAAD10 that had external routing and exposed cables below the down tube, I say that shifting performance degraded after about 2-3000 miles. I attributed this to all the dirt and gunk that gets kicked up by the front wheel while riding in rain that gets on the exposed cable under the down tube, and pushed into the housing. I tried higher quality cables and housing, and they didn't seem to last much longer to justify the increase in price. So with cheap cables, it usually meant swapping shift cables 2-3x per year, and housing and brake cables once per year for 8-10k miles per year riding on that bike. Not that big a deal since the cables were so cheap, and external routing is super easy. It cost me about $40 to swap cables and housing on that bike annually, and maybe about 10-15 minutes per shift cable swap, and 45 min for the full housing swap which includes doing new bar tape.
My new road bike is a 2018 R5...and it has the shifting cables enter the frame just behind the stem on the top tube. Which is dumb, because even though none of the cable is exposed externally, where the housing enters the top tube is where all my sweat drips...and I'm a heavy sweater in a humid area. I had the original Shimano cables that the bike came with and I went a full year with perfect shifting, but decided to swap the cables and housings just because 1 year seemed like a long time for me (about 7k miles). Decided to go with cheaper cables and within 6 weeks shifting performance sucked really bad. When I pulled the cables out, they were completely orange in that section where the cable entered the top tube because they lacked that coating that more expensive Shimano cables come with. So it's back to more expensive shift cables for me on that bike. Cheap brake cables still work fine since I don't sweat on them, and the cheap housing is also fine since more expensive housing isn't going to prevent corrosion on the cable. In the long run the more expensive shift cables will probably end up being cheaper, improve performance, and save a lot of time and hassle from dealing with internal cable replacement over and over again.
My new road bike is a 2018 R5...and it has the shifting cables enter the frame just behind the stem on the top tube. Which is dumb, because even though none of the cable is exposed externally, where the housing enters the top tube is where all my sweat drips...and I'm a heavy sweater in a humid area. I had the original Shimano cables that the bike came with and I went a full year with perfect shifting, but decided to swap the cables and housings just because 1 year seemed like a long time for me (about 7k miles). Decided to go with cheaper cables and within 6 weeks shifting performance sucked really bad. When I pulled the cables out, they were completely orange in that section where the cable entered the top tube because they lacked that coating that more expensive Shimano cables come with. So it's back to more expensive shift cables for me on that bike. Cheap brake cables still work fine since I don't sweat on them, and the cheap housing is also fine since more expensive housing isn't going to prevent corrosion on the cable. In the long run the more expensive shift cables will probably end up being cheaper, improve performance, and save a lot of time and hassle from dealing with internal cable replacement over and over again.