Just an FYI, as I have said classes 50 & Relic with full DL (including both tanks), Blm and Brd have a lot of front loading in their DD. Especially Brd. As an example, a Brd with proper sub classes lvled has *5* CDs to blow at the start of most fights. You can argue them to wait, and for new tanks especially they probably should, but on most tanks/fights it is optimal for them to blow said CDs so they are used more then once a fight. I personally wait to have at least 2 CDs (Internal release especially) to get my DoTs out, which is basically the start of ST rotation, and overall DPS. Then I am pulling out Bloodletters as I get procs (at least a couple procs within the 14sec. DoTs), and crits also play a factor.

All in all, even Relic tanks I have to throttle hate on a lot of time. Every Brd/Blm should have Quelling Strikes if they are geared and know their class. Blm can be the same way. Depending on crits, and firestarter procs (free Fire III) you can really jump in hate quick on the Tank. I find with quelling strikes Blm is a bit easier to not surpass the tank in threat if they are doing their rotation right. You will always be pushing the envelope a little, but Brd (especially in first 1/4 of boss' health) can really just go overboard. Either way, I always wait ~5 seconds or so before I even start DDing and don't think I've ever heard any tank complaints.

As a fellow tank, just make sure you are doing your rotations well. If a DD is just decked out in gear, Berserk definitely might be a good option early in the fight. Make sure you are pulling/running in with Tomahawk > BB combo > BB combo > SE combo to establish threat. You really shouldn't have an issue with 95% of DD if you are doing that (especially with your Relic Axe, you shouldn't have to +1). To be honest, you might even consider doing BB combo x3 if you see the Brd/Blm really riding your threat at the start. After that time their Buffs will have worn off, and you'll get some more substantial threat lead.

TL, DR; Blm/Brd have huge front load potential. Threat combos/buffs should keep you ahead if you are relic.