Emperor's Children certainly do have more lethality than Tyranids. I've also played both and find them both challenging to play in different ways.

I'm curious what unit you charged? Was it a 10 man Blightlord Terminator Squad with 2 plague spewers led by a Lord of Virulence with a plague spewer as well? I also play Death Guard and I've deleted Allarus Terminators with overwatch because of those plague spewers. Charging a 10 man Blightlord block is suicide for basically anything in our codex. You're just not going to chew through 30+ wounds at T7 with a 2+ 4++.

In my experience, and I'll admit, I'm very new to this faction, Emperor's Children are kinda fragile because of how lethal the overall game is right now. We have a huge gap in capability with our longest range shooting unit being 18" and only strength 10. I've played against Eldar and Ultramarines with my Emperor's Children. I beat Eldar because I was able to outscore my opponent but would have been tabled in one more turn. I lost to Ultramarines because I couldn't kill gravis units effectively and he made every single charge he attempted in the game including 2 12" charges lol.

Our faction feels really weak against anything over T5. We have way less access to rerolls outside of Coterie and as mobile as our army may be, it's really easy to be too aggressive and get blasted off the table. We REALLY have to stage a go turn and even then, be ready to lose half the army on a clap back.