I dunno, a small DPS boost and better overall survivablility sounds exactly like what a strategic cruiser is supposed to do. Its not going to be cracking most battleship tanks but its a mean little cruiser.
Um. Actually. A well-fit Proteus with decent skills (lvl 3 ish in subsystems and 4-5 on support skills) can break a single well-fit BS' tank quite readily. While tanking harder than a BS. That said, any cap issues and you're screwed - the focus on DPS and tank really makes the ship's capacitor longevity plummet.
As for the Tengu thing, as a PVE boat their advantage over the Drake is the actual speed at which they move and the ability to either sig (speed) or shield tank all but the heaviest hitters. As PvP boats they are decent alone but really shine as part of a larger fleet. The point of a T3 is to be versatile - they may not do things as well as a comparably priced T2 cruiser, but they do a number of things competently.
As for the 6.4% damage boost, that is actually a significant boost in applied damage. Remember that a 5% per level bonus to resists for Amarr and Gallente has been deemed too strong by the devs and reduced to 4%/level. EvE truly is a game where a few extra percentage points really make a difference. The 10% damage bonus is actually
inferior to the combined dam/ROF bonus - which is why with Odyssey a number of Gallente ships, for example, are having their flat damage bonuses replaced with a ROF bonus.
I reiterate that the point of a strategic cruiser is
versatility. It has
slightly better DPS...AND
slightly better tank. AND it's smaller. AND it's faster. You're currently complaining about getting FOUR almost straight upgrades to one of the strongest battlecruisers in the game! Are they HUGE upgrades? No! A significant damage upgrade would be to, say, a Raven with Torpedos fitted - but at the expense of being far easier to hit due to your slow speed and much larger size.
You have gotten yourself into the trap of thinking that bigger = better in EvE, which is a very carebear mindset to have and is the number one reason for the endless complaining on the forums about how the much larger Mining Barges can be killed by a few small destroyers. If you want THAT, play WoW or any of the other insufferable themeparks out there.