It is common with most internet users that their routers are the first thing at fault every time an issue occurs. However, try upgrading your internet speed or plan instead of blaming the router and buying a newer one. Yes, buffering mostly happens when your internet speed is slow and is not receiving the data from the other end on time.
Therefore, to cover that time-lapse, it needs to buffer and start receiving data to play that particular video again. Especially buffering happens when you watch an HD or 4K high-resolution video. So, instead of buying a new or better router, get a fairly good router with a good internet speed and see how it makes a difference.