You're comparing a noncaster with casters and pseudocasters. Not really a fair comparison there. I was never arguing the dragon shaman's power level, just the fact that they aren't actually more boring or incapable compared to other similar classes. I could argue about your characterizations of rogues and monks, but you said nothing about how they are more interesting than the dragon shaman other than the rogue does more damage, with a lot of work.
You can stack the effect multiple times on the same breathe. You can make it last as long as you want with the corresponding number of rounds of delay for your next use.
While I did mention breath channeling feats in my original post, clinging breath does allow those affected to take a full-round action to attempt another save to remove the effect and with a +2 if they drop prone
Entangling Exhalation allows your breath to do half damage initially and then 1d6 per round of entanglement. The half damage would be maximized, but the original example was clinging breath and not exhalation.
You should reread the stacking rules for metabreath feats. You don't have to take the feat multiple times; you just use them multiple times on the same breath, stacking the effect and penalty.
Clinging breath doesn't halve your damage, it does half the damage every round after the first. The whole point of the heighten is to make it incredibly difficult to simply remove the effect or reduce the initial damage in the first place (which subsequently reduces the damage per round). So if I had CON 20 and heightened to +5, the total delay in rounds until I could use the breath again from my example is 1d4+17. Though, it would be unlikely that I'd need to use the breath again after that.
You can do a whole bunch of different things with dragon shaman based on their unique mechanics just like you are doing with all of those.
Ubercharging is only fun if your DM only ever gives you flat fields and never any difficult terrain or obstacles. Not to mention all the the ways tanking your AC can be heavily exploited to flat out kill you BEFORE you attack. Dragon shaman can pump intimidation too as it's a class skill. PRCs are fully under the purview of your DM. Never are you guaranteed to have a PRC nor are splatbooks the only source of legal PRCs. In fact you are even encouraged by the DMG to design and tailor your own for your campaign.
You don't need a feat to charge. The only thing that makes ubercharging stand out is that a barbarian ACF grants a feature more powerful than an epic feat at level 1. Otherwise, it's literally just charging with more attack rolls.
Baseline the breath can be used after 1d4 rounds. If you roll a 1 there is no delay as durations end just before the initiative count they were started on. And while dragon shaman can forego the likelihood of multiple breaths, it can provide a lot of damage and options for that one breath that the DFA just can't (unless you are allowed to pick up metabreaths).
DFA is inherently a selfish class. Everything it does is for itself. Sure it gives you a more breath focused experience, but at the same time you miss out on the PHB2 auras, draconic adaptation, touch of vitality, medium BAB, and armor proficiencies of the shaman. Ultimately they are just completely different classes that fulfill completely different roles and playstyles. To say that DFA is the class that fulfills the dragon breath maniac fantasy is true, but dragon shaman was never intended to be that so comparing the fantasies just doesn't work.