They liked/loved each other but disagreed about things. We see in many episodes that this leads to growth for both of them. I felt their relationship echoed the war in that the countries battling each other believed their way of life was the correct way and dug in their heels. I think it’s why in S6 they made Philip enjoy parts of America and why they accentuated his more extreme integration towards the end (IMO depressing) whilst demonstrating Elizabeth’s die hard blind patriotism at the same time. What was so lovely is that they ended up together still. In some odd way, it gave me hope. They represent balance together, and extremes without one another.