The problem is that your LAN connection to your PS4 is still half-duplex wireless no matter how fast your WAN is. Further, your wireless signal is susceptible to channel interface, microwave interference, ham radios, etc...the same as anything else traversing the air.
Unless you're running a real-time monitor on your connection, you have no way of knowing if you started off with a good connection at the beginning of the match and encountered some interference mid match which would have negatively impacted your connection mid match resulting in lag and poor round trip results as when you start a match, the signal indicator is only a snapshot of your connection.
A 5 MBPS circuit running (while not suitable for gaming imho) has a higher rate of predictable performance then your wireless connection...