I agree that the two hit may be worth more. But if you increase the cost, of heavy armour/cyber then marauders become the cheapest and no-one ever buys elites with armour.
At the moment, only Hazat can buy both elites and marauders. That might change, but anyone who can is already spoiled for choice - they can upgrade cheaply for offense (elites) or defense (cybers), specialize in defense (elites with blur suits and heavy armor), or get marauders who do both fairly well. They don't really need the heavy armor-only elite option to be cost efficient, leave that to Li Halan who don't have a marauder option anyway. I do think they get too much for the point cost with cybers, as everyone does. The real problem is that elites are too weak for 2 points but have locked up the whole system already. If they were 1 point apiece, or +2 to hit at 2 points, the costs for attack and defense could be more reasonably balanced, with 2-hit assigned a nominal cost of 3.
5-point spread of upgrades too small to cost troops in a balanced fashion?
Possibly - the best you can do is try to make it roughly fit a statistical basis, and even there you have lots of inobvious stuff to take into account, not least of which are oportunity costs. Cybers probably don't thrill most factions, for example - but poor Al Malik had no upgrades at all before they came along, and neither the ukari nor gannock are nearly as helpful for boarding defense, which is what they need most. As an Al Malik player I'd happily pay 3 points for Cybers - at 2 points, I feel like I'm exploiting a flaw. Most other factions would probably prefer to buy marauders, or specialized elites, depending on how offensive they feel about boarding.
I meant in my own fleet, for every destroyer I'd take at least 3 frigates to support it.
Whatever works for you - frigates are certainly more versatile than galliots or raiders are, since they can both shoot and board reasonably well for their cost. Destroyers shade more toward shooting, but are tough enough to make troop upgrade investments more reasonable, which can also let them launch (or defend against) boarding actions as well.
Should be interesting to try cruisers and dreads - I'm tempted to simply proxy rather than wait.