Plasma cannon is nice, but if I had to choose between plasma cannon or locusts for Apogee, I would use Locusts with Expanded Missile Racks and Mining Blaster over Plasma Cannon. (I do not need to aim for Locusts, and blaster will be anti-armor against pirate orbital station.) That said, I would dump missile racks for both plasma cannon and locusts.
What makes Apogee good beyond heavy weapons is its overall package at a bargain DP price. It is cheap (only 18 DP), has tough shields, and has good campaign stats. It is not a combat monster, but it is a good fighter for its cost, and has unusually high campaign stats for a combat ship. Plus, it gets surveying for free. It usefulness wanes late in the game, but it is still a good ship anytime in the fleet until after you survey every last planet in the sector. It can fight, it can tank, it can haul, it has surveying, and it is cheap for a cruiser. At its best, Apogee should be worth about 20 or 22 DP.
As for Venture, if I am desperate for a meat shield very early in the game, I could find and bring one. However, I always start with Apogee (except for one game when I picked Hammerhead instead) and skip the point in the game where I might need a Venture.