You can help your FC mates, even if you have to carry them. I'm not on a great connection, nor am I "hardcore", but I managed to clear Titan HM with relative ease after learning the fight (i.e. joined a learners run in PF, my suggestion is to make one on your server to help people learn the fight).

It may be that they don't know the patterns since it's a dance fight like Demon Wall in AK, or it might be lag as you say (or a bit of column A and a bit of column B). Phase 5 of Titan HM can be done with 4 people alive (1T, 1H, 2DPS), assuming they know the patterns (or have very good reaction) and the healer can keep up.

It is upsetting that people can't clear the fight, but it's understandable. The way the fight is designed might be the issue I think, not exactly player skill. It's a very specific pattern with randomness mixed in, it's not hard to mess up on the fight and eat a landslide or plumes; especially with lag.