Constantly losing aggro

Time: today, about 12:00 GMT
Frequency: constantly
World name: Moogle
Character name: Credor Beeman
Class/Level: Marauder/28lvl
Area and coordinates: Hauke Mannor
Steps:
1. group of mobs, I pull with Tomahawk, then 2x Overpower, then start rotating enmity combo on one mob
2. BLM (synced down, ilvl 30) start casting Fire on that same mob
3. after two enmity combo rotation I started losing aggro

Situation repeat with next group of mobs and so on.

This is something not balanced in game or enmity building problem?

Marauder is my new pofession, I play mainly PLD iLVL95. After the patch 2.3 I feel that enmity is less stable, but today in Hauke Mannor with Marauder I can't tank at all.

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MRD is extremely disadvantaged at that level until it dings 30, becomes WAR, and gets Defiance (hate stance) and Butcher's Block (3rd and most potent part of your single-target enmity combo). You're reaching the point where Skull Sunder alone just isn't going to cut it anymore against a competent (and higher level) DPS.

If you insist on tanking that dungeon I'd suggest waiting until then