Question about stacking damage bonuses

Ok, so I've been looking at 2 separate builds.

The first one is a Celestial Warlock which uses True Strike + Agonizing Blast + Radiant Soul (the level 6 feature from Celestial Patron) to stack their CHA modifier 3 times on the same casting of True Strike, for a whopping +15 at 20 CHA.

The other one is a Path of The Giant Barbarian, for which I'm being told that Giant’s Havoc: Crushing Throw (which adds your Rage damage to thrown attacks) is utterly useless in 2024 because you already add your Rage damage on all attacks with melee weapons (which wasn't the case in 2014), and you can't stack it so the feature has literally no effect.

Am I the only one feeling that the caster is getting some really unfair favoritism, here?
Even though Path of the Giant was released before 2024, that double-standard makes no sense to me.

Quote from Natrel >>

[...] The first one is a Celestial Warlock which uses True Strike + Agonizing Blast + Radiant Soul (the level 6 feature from Celestial Patron) to stack their CHA modifier 3 times on the same casting of True Strike, for a whopping +15 at 20 CHA. [...]

 Just note that's only if you assume the damage from True Strike comes from the cantrip, or more generally, if you or your DM think True Strike and Agonizing Blast synergize at some point. In my opinion, Agonizing Blast does not interact with True Strike before level 5.

I asked a similar question using Fire Bolt, but True Strike was also mentioned in the conversation: Agonizing Blast + Radiant Soul

For fairness, other threads with different or similar opinions:

• True Strike and Agonizing Blast
• Does Lessons of the first ones, Agonizing blast, and Magic initiate (Druid) work together to create the best melee weapon?
• 2024 Evoker Wizard, Potent Cantrip and Weapon Cantrips
• Understanding Magic Stone and Agonizing Blast (2024 version)
• Agonizing Blast and Booming Blade
• Potent Spellcasting/Cantrip + Radiant Soul
• True Strike + Agonizing clarification
• True Strike Question for the Hive Mind
• War Caster + True Strike
• Warlock 2024, taking Agonizing Blast twice at level 2
• True strike and Arcane Grimoire stack?  
• True Strike + Potent spellcasting 
• 2024 True Strike and Extra Attack
• Agonizing Blast can apply to which cantrips?

Quote from Natrel >>

The other one is a Path of The Giant Barbarian, for which I'm being told that Giant’s Havoc: Crushing Throw (which adds your Rage damage to thrown attacks) is utterly useless in 2024 because you already add your Rage damage on all attacks with melee weapons (which wasn't the case in 2014), and you can't stack it so the feature has literally no effect.

I don't think there is anything anywhere in the rules that says your Rage Damage Bonus can't be added twice to the same damage roll by two different features.