That's definitely hard to say, since both reasons you mentioned are valid. When I played on EU servers with a shielder, I had to turtle up much more than what I was used to before. It might be more fun to use other melee classes or play support such as a hoplite. As long as you're careful, I found cav to do decently well with higher ping as long as you don't attack other horses head on that often. I would at least try shielder for a bit and see if it works out in the end.