I think it's generally accepted that troll warbeasts are expected to have Rage on them in order to trade effectively with other factions. I believe this creates a problem with the way that trollbloods function on the table and in their design.
I don't actually mind that Trollblood beasts are a bit below average in the P+S department. What I mind is that there is really only one solution to buffing troll warbeast's melee damage in faction. Designing models with the expectation that they will include rage instead of include melee damage buffs is what I see as the actual "rage problem."
By expecting rage, and only rage, to be the primary in faction damage buff, it heavily impacts faction design across multiple factors: Animi, Spells, Feats, Statlines and Play.
Animi: In MK II, Slag and Pyre trolls could be used as buff bots, to provide damage bonuses to melee infantry and warbeasts outside of rage. With the loss of these two options, rage becomes even more important to troll gameplay, and restricts freedom of choice in list design. The expectation that rage is what will provide the damage buff limits opportunity for new beast design, and causes conflict with other useful animi (as noted in Trollock's Is Rush the worst animus in trolls? thread)
Because you need to buff in order to trade effectively against enemy models, and Rage is the only non-limited damage buff animus available to trollbloods, it forces players' hands in list selection and causes what could potentially be useful models to not see table time.
Spells: Among troll warcasters, there are only 4/17 damage boosting spells (and one damage boosting ability for Calandra). Two of these are debuffs (Calamity and Mortality), one is only effective against already buffed enemies (Spellpiercer) and only one actually provides a direct damage boost to warbeasts (Pulverizer), with Calandra's Fate Blessed serving as a reroll based Damage fixer.
In terms of spellcasting units, only the Dhunian Knot provides a damage fixer via puppet master.
Again, I feel that the expectation of Rage providing the necessary damage buff, instead of giving it through multiple sources, negatively impacts the play experience of the faction. And given that Rask has access to both Rage (through Wrastler) and Fury, there's little reason why the spell lists for troll warlocks can't include more damage buffs of their own.
Feats: 5/17 warlocks provide damage boosting feats: Borka1 (sort of), Calandra, Horgle2, Madrak1, and Madrak2 (sort of) , usually thanks to improving dice rolls. Dice roll boosts isn't unusual as far as feats go, but given that trolls tend to have lower base damage, they have much farther uphill to climb in order to meet the same level of expected damage to which other factions have access. There are no Troll casters that provide flat number bonuses to Strength or Damage.
Statlines: As stated before, troll statlines suffer from a lack of base power. Our highest damage non-character heavy only has base P+S 16, and none of our beasts (colossals included) break base P+S 20. Compare to say, Khador (who has multiple warcasters with access to Fury) with their P+S 23 base colossals and 12 pt. P+S 19 Juggernauts.
The argument could be made that we have the potential to reach higher numbers through buffing, but the biggest swing that can be made in trolls is +6 P+S, and only available on one caster, meaning that we have only one way of even matching Khador's heaviest hitters.
While I've only got incomplete math to go off of (I need those full card PDFs bad, PP ), it seems that every faction caps out at roughly the same numbers for P+S, but trolls start a little lower and require more investment than other factions to hit those numbers.
Playstyle: The reliance on rage as a damage buffing mechanism also has significant impact on the playstyle of the trollbloods. Rage is only found on two very expensive centerpiece models. The Mountain King is a Gargantuan, and has everything that comes with that while the Mauler is our main melee brawler. Committing either of these pieces to the fray means you risk the biggest (and possibly only) damage fixer you have, while keeping them back in order to protect access to their animus means that you're wasting a huge number of points on a single spell. This is a very tricky tightrope to walk, as losing your rage source can easily mean that you've lost the game altogether. The expectation of committing your primary buff provider to melee where they are at the greatest risk of dying is something I think is ultimately a major negative aspect of playing trolls.
I think that what needs to be done to fix this is that trolls as a faction need access to more damage buffs or ARM debuffs. Centralizing the troll battle plan around access to rage is limiting and creates an extra layer of weakness not present in other factions.
It is fine if Trolls are the "STR Buffing" faction, but in order to be the STR Buffing faction, they need access to more than one STR buff.
Just like Khador is the slow faction that has access to lots of speed buffs, or Cygnar is the fragile faction with lots of access to ARM buffs, there's nothing inherently wrong with being a faction that needs to buff strength to level the playing field. What is wrong is how limited the access to those strength buffs are, and where they are located.
If privateer press brings back the old Pyre and Slag animi, opens trolls up to more damage buff spells on warcasters and maybe brings in a damage buff on a spellcasting unit, I think trolls will see a drastic improvement in the variety and efficacy of their play.