Can someone explain how invasion is supposed to be fun?

I enjoy it. I am on 32/65 (last tier) and have only suffered 2 losses. You really have to be creative with how you play and when to take a hit or cast a spell. I am using Mang, siegebreaker, Flame Troll and Infernus.

Same. After 5-10 battles just had to ā€œovercomeā€ instead of enjoying the process. I donā€™t even care about rewards anymore, so boring this process had becomeā€¦ same battles over and over and over again while enemy stat numbers growing bigger. Ought to use the same weapon, same team, same approach for each battle. Iā€™m OK with 5-20 similar battles, but when everyone in active guild had to do 200-500 battles so that the guild can collect rewards, thatā€™s way too much.
I think 5 different bosses (along with minions) for each raid, which require different approach for each battle, could be more fun. Delves already represent something like this, but you canā€™t change your team there.