1) Yes it is, or some other FFXIV-dedicated forum full of nutcases. Take this stupid ass argument to any general MMO forum and be laughed off as an imbecile. Honestly.
2) Yes. Mighty heroes should never jump. I mean, it'd ruin the immersion! I can't even jump in real life!
3) Yes. I have. Let's take WoW for example... Jumping has no effect on combat, except breaking your spellcast, same as if you moved. It has no other battle potential. There are ABILITIES that can help, such as disengage, but they're not normal jumps. Just because people are jumping doesn't mean it DOES anything, in fact, it lessens the control you exert over your character because you're moving in a straight line with no Y or X-axis control for a second or so, with no increased speed.
4) Jumping doesn't lag the game in that case or in any other. My god man, what the hell are you on about? I'd think it's the battle with 30+ players and spell effects AND NOT THE JUMP.
Holy damn, the ineptitude of these arguments is pitiful.