I mean, I have my own strategy , and immortal ain"t that hard for me now or better said it is as hard as I let it be, I could probably play on deity if I wanted to . I guess that the strategy you speak about is that they simply get some advanced units, spam them and try to kill you ? I mean that sounds just as boring as seeing the AI manage naval combat (or combat in general most of the times).
I think it is much more complicated than just spamming units and rolling you over.
Land is a huge advantage so if you have great land or space and you know what to do you are going to most likely win.
However the Diplo Game is completely different because its real life Diplo.
You may work together with your neighbor and team up against the stronger player.
You will get stabbed in the back as well so you have that problem.
I think the best thing with this game is the rotation.
You play Single Player till you get bored.
Next you play GOTMs or shared games.
You get bored with that you play some 1v1.
Bored Again you play 6 to 12 Player FFA.
If that bores you, you can play team games like 2v2v2 or 3v3v3.
Get bored with all that and start recording your game and uploading.
If you enjoy Civ you can rotate this constantly always keeping things fresh.
The main thing is you have to jump into MP and try it and keep with it for hours to see if you like it.
The game is always going to be about Domination in MP because it is the fastest and easiest way to play.
Nobody is going to let you turtle up and win any other victory choice.
Personally I was only in two games that were won by a very quick, sneaky Culture Victory.
That is with over 8,000 hours of MP games that I have played between different versions of Civ IV, V and VI.