If any ship gets its points back on a cannon investment, it's the Defender. Turning around is so trivial and combined with its toughness you'll be getting a lot of shots out of that cannon.
4 dice at range 3 where the defender doesn't get an extra defend die is DRAMATICALLY better than 3 attack dice. Well worth the 7 points in my opinion.
Slap an HLC on Vessery and he becomes an unholy engine of destruction.
My problem then becomes determining where to pull the 7 pts from. So far, my list is undefeated out of 7 or so games. I'm not sure what I would take off to get that HLC. Those 7 pts are really tough to find room for. That's the point of the OP, as well. I'm stating that it's OK to not use HLC on Col. V.
I'm not saying that HLC are bad, but they aren't mandatory.