Seriously. Triple or double. Discs or double pivot brakes. Tektro or Shimano. Now Tiagra or 105. At a certain point, you need to pick the bike that fits you and suits your riding style. No bike is perfect, but many bikes in the $1,200 to $2,000 retail are marvels of modern technology. Light, responsive, reliable even reasonably comfortable. Are they perfect? No. You might need to change out a saddle, or brake pad, or chain down the line.

To to answer your question, Tiagra works very well. I posted a chart on one of your threads. Current 10 speed Tiagra is the same as 10 speed 105 of just 4 or 5 years ago. Even 9 speed Sora or 8 speed Claris would work well for years. That said, a bicycle is a long term investment so if you can swing it, 105 is better.

but, it makes no sense to buy a complete bike only to swap out the complete group set. If you really feel flush, consider getting some custom wheels. Or just ride your new bike for 2 or 3 years as is.