True skates are heavy. There is no getting around it. You say you knew this going in, yet are surprised? Not entirely sure I understand that....
Anyway.
If you're asking 'why' they're heavier, it's mostly because the entire True boot is made of heat-moldable carbon fiber weave, while skates from Bauer and CCM use thermoformable composite plastics. True's carbon weave is MUCH stronger than the plastics used in other skates...but it's also quite a bit heavier.
Also, steel makes a big difference - particularly now that all True skates ship with Step holders and Step runners. For all of its wonderful qualities, Step is notoriously heavy steel.
In the end, there is absolutely a trade-off; comfort, protection, and performance vs. weight. Is it worth it? The answer to that will necessarily vary from player to player. For me, it's worth it. For 68 NHL players, it's worth it. For your son? Only he can answer that....
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N.B. By way of comparison, my Trues with a size 272 Step holder and Step Blacksteel runners are 21.8% heavier than my old Bauer TotalOnes...
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Edit: Many people have fit issues (Haglund's Deformities, unusual foot geometry, flat or high arches, bunions, extreme pronation, etc....) that make off the shelf retail skates a virtual impossibility. For them, even the lightest skates on the market would feel like they weighed a metric shit-ton, simply because they'd be so damn uncomfortable. When the choice becomes a skate that weighs more vs not being able to play at all, most people will choose to deal with a few extra grams....