I consider myself an extreme purist when it comes to space marines. the fluff makes it clear that you should be looking to your escorts for ship cracking, and leave the boarding to your cruisers.
Strike cruisers are awesome they way they are. If they keep on getting krumped, maybe your using them wrong.
Allow me to make my point firm.
1. It says quite CLEARLY in the writeup that the space marines were systematically neutered in space after the Horus Heresy, and rightfully so to prevent it from ever happening again. standard cruisers and lances outside of escorts are not allowed under any circumstance. (don't give me the black library garbage, we all know they pay zero attention to cannon)
2. It also says that strike capacity is restricted to escorts... if you hadn't noticed, their escorts are amazing. If your having problems with your fleet, take less strike cruisers and more escorts!
3. The most damning thing about the fleet composition is how it describes chapter variation... Some strike cruisers may look different, but on the whole, no chapter has any sort of special ships, technology or advantages over any other. All strike cruisers and barges are made to a standard kept strict by the Imperial Navy and the Inquisition. Your precious ultramarines are just not that important in space, nor are space wolves, Dark angels or black templars. If you want your fleet to represent your 40k army, build your fleet to match their style, and paint it in their schemes. don't forget that at this scale, your armies are in the 3-4000 point rage per strike cruiser, and 10,000 point range for the battle barges... at that point there just isn't any difference in the damage they can dish out.
4. According to the rules, thunderhawks take up 2 ordnance slots instead of the normal 1 that a fighter, bomber or a-boat would use. Every strike cruiser TECHNICALLY has launch capacity 4. If you give a light cruiser the ability to launch 4 thunderhawks, you are giving it the same launch capacity as an Emperor battleship. PLEASE justify this insanity to me.