Its definately not due to your glove enchant. In 5mans sometimes even on my paladin I dont always glue aoe mobs directly onto me, theres a number of reasons for this but usually it comes down to overgeared dps just nuking.
I dont have any kind of threat problems in raid settings, but the way 5man instances work nowadays, is mobs die insanely fast, so people just go all out, my general idea of tanking 5mans is that im just there to lead, I pull the mobs, contribute dps, but in the end, threat isnt super important since they die so fast, if someone pulls, just taunt back. if they are pulling on purpose or whatever, ask them to slow down or quit what they are doing.
I just tend to let the melee facetank these kinda instances while ensuring nothing goes horribly wrong, You are probably doing just fine. the 2% threat decrease from armsman is so tiny that theres no way you would notice it. if you were previously only sitting 2% higher than the dps in threat then theres other problems that a chant alone cant fix