From looking At the lists I can understand why you felt a little overwhelmed, your opponents list was more competitive than yours. Even though you had a fun list to play, and you included good choices such as a Slann and a Carnosaur your list could be improved if what you are looking is to play more competitively.
I hope this short text would help you a little with it. Although there are some units in as that are very good by themselves (stone horn, zombie dragon, tree lords, attributors, storm fiends, etc...) AoS is a all about synergies and making your army work as a whole instead of separate units doing their own thing (there are only very few cases where this works).
Seraphon are not the exception, in fact they are actually one o the armies that need synergies to really shine. SO my suggestion to you would be to explore how those synergies work and that would help you understand what seraph can really do. Some examples are the following:
- 2 Carnosaurs, Skink Starpriest, skink priest, Astolith bearer ( each gets 7 bite attacks rerunning to hit an causing damage 6 on wound rolls of 6+, retooling charges and saves).... can be improved even further with a slann and a battlemage
- Kroak on a vortex with an astrolith bearer and some ripperdactils in shadowstike (croak mortal wounds key elements on the tabletop wile rippers take care of larger threats such as a zombie dragon)
- Eternal starhost, with skink starriest, astrolith bearer and skink priest save of 2+ resoluble ignoring rend with d3 damage on the pole arms and 2 damage on the bites when rolling a 6+ to wound, add to that a grup of razordons and the only option for your enemy is to use mortal wounds agains them or leave them be
this are just a few examples of the top of my mind but as you can see command abilities, battalions and hero supportt really helps your army get together and really show what it is capable of doing.
Since the generals handbook came out I have played many games against a death player and I have yet to loose or to feel that my army was on a disadvantage so I think is just a matter of getting more games in and learning what you really like to play and how to make it more effective. with a little bit of research I think you will find what you like:
Some of the most popular competitive options for seraphon are the following:
- Skink Starpriest
-Big blocks of Saurus warriors (40)
hope this helps