Stripped of everything that can be stripped, a Stormcrow is going to have 32.5 tons available and the Summoner 32.0 tons. Stormcrows can carry up to 9.64 tons of armor at most and Summoners 11.31 tons. So with max armor, the Stormcrow has 22.86 left and the Summoner 20.69. It's common practice to shave some extra points for even tonnage, so consider the Stormcrow to have 23 tons available and the Summoner 21 tons.
However, the reason the Summoner has so little available for a 70 ton mech is because of permanently mounted equipment. There are 4 heat sinks in the engine and 5 jump jets that cannot be removed. The extra heat sinks in the engine work to keep the mech cool. The jump jets are a huge help in getting over obstacles other mechs would have to go around.
If you're going to compare the SMN-D to the SCR-Prime then yes, the Stormcrow is faster and has an extra medium laser. However, the Summoner has a targeting computer to make the lasers it does have better, machine guns to help in close-combat brawls, and twin AMS systems to counter LRM strikes. So is the Stormcrow actually better?
I currently have one of my favorite Summoners outfitted as a missile boat. (
SMN-B) To be honest, I can easily do the same thing with a Stormcrow if I wanted to, and add a TAG to the mix. (
SCR-D) However, that is not just at the cost of the jump jets, but also heat efficiency. My Summoner handles hotter environments (Caustic Valley,
Mordor Terra Therma) a lot better than the Stormcrow can. The extra heat sinks do help.
But to be honest, I don't see the Summoner being anywhere close to a top-tier mech anytime soon. The real reason I pilot one is because it was available for C-bills before the Stormcrow was. Also, there have just been too many people dropping with medium mechs compared to other weight classes. So until things start calming down (and I build up a stash of C-bills again), I don't expect to be getting my Stormcrows anytime soon.