Well that's a lot of text...
It would be nice if there were more approved Tyranid lists, but that takes playtesting. TacComms is 90% opinions and 10% playtests though, so here we are.
I'll start by saying some corroborating information (what you used, what the table looked like, how you activated your formations) would be helpful for a lot of this. Some elaboration would be helpful too. Starting a post with "this list makes no sense" isn't even slightly helpful. If it were, I would respond with "yes it is" and call it a day. Instead, I'm going to refer to the playtesting that was done with this list (of which there's 75+ relavent
battle reports) to back up what I'm coming back to you with.
Spawning has been around for at least as long as I've been here. It's not a quick fix, and the current system is probably the weakest version of it the nids have ever seen. On average, a formation is returning 1-2 gaunts per turn with it. It helps a bit to keep formations in the game, but honestly that's more the rally bonus more than anything else. What swarming and the rally bonus are reinforcing is you have to kill the synapse creatures to effectively stop a nid army. That's how they work in the fluff, "shoot the big ones" and you have a chance. If you don't kill the synapse, you can expect the swarm to be back in the game in a turn, and at close to fighting strength another turn or two after that. If you don't think that's tyranidy, OK, but that seems pretty close to the fluff I've read.
On the close combat stuff, sure six bases of marines can break a lot of Hormagaunts in a FF. But why were the Hormagaunts in assault range? If you leave them within 30cm of the Marines, I'd expect them to be engaged. If they're between 31 and 40cm though they can engage the Marines in CC while all the Marines can do is kill a few of them and place a BM. I'll also add the swarms can be (and are meant to be) mixed. Add the AV bugs, Gargoyles and Termagants. Make them multi-use. Putting all your eggs in the CC basket is going to see them engaged in a FF by your opponent.
Given that I've taken Hormagaunts and Warriors in every one of my games and gotten the Hormagaunts into CC I don't see how they can't use their infiltrate ability. Keep them in back and the FF bugs in front. The FF bugs help when you get engaged in FF, and can be used for coherency for the Hormagaunts when the bugs engage. If you can keep the FF bugs outside of 30cm but within 35cm of the enemy you can also engage without being engaged yourself.
Malefactors have been a very common BTS for me. If you're leaving bugs in them, then yes you can expect them to die when the Malefactor dies. Unless I'm facing tons of BP weapons though I don't leave them in. If an enemy wants to shoot the Malefactors there's a 75% it'll save against a regular AT hit. I don't see that as giving away a free kill.
Lictors are 50 points because they can teleport, engage 40cm into CC with two enemies thanks to infiltrate, and attack with a -1 to the enemy's save before anything gets to attack them. They're one attack because we found two too powerful, and because they're one lictor not three raveners on a base.
An all Carnifex formation would be good for an AV list. I don't think it has a place in the base list. 50 points is on par with a faster Wraithlord without a shooting attack.
Dactylis have been playtested heavily in our group. Their cost scales similarly to other artillery formations. They cost more because they're initiative 1+ and have 4+RA for armor.
Put the Harridan in front and the Gargoyles in back. You get four extra 5+ FF attacks and outnumbering help for 80 points. Yes they're good at grabbing objectives but they're TK bait.
If the 'phant sucks, post some games and show us how. It's 175 more points than a 'dule which gets it bigger TK in CC, some FS CC attacks and the 2DC.
Same with the stealers. Use them to screen for teleports, keep them between 31 and 40cm of the enemy and you get your FS attacks on 2+.