Well now.
Level 18, you say? No SOs yet, then. I've found my Fire/Dev to be very strong indeed but, as with many builds IMO, you really need SOs to see the full potential of the powersets.
Before I start making any assumptions, however, could you post your build? I'll offer whatever pointers I can.
Check this out, it may be of use.
At lvl 18 I have;
Fire Blast
Fire Ball
Fire Breath
Fire Rain
Web Grenade
Caltrops
Targetting Drone
Swift
Health
Hasten
Superspeed.
By 28 I expect to add;
Blazing Bolt
Blaze
Trip Mine
Cloaking Device
Stamina
... and of course SOs.
Its just im not going to spend 10 more levels worth of time, on something which doesn't deliver what I expected when i set out. Obviously in the current guise its all about he AoE. Which on Cherry Hills is like self power levelling. However, with mob scaling, it seems the AoEs really get quite poor. Appreciating that SOs will make a difference, but then the Mobs seem to scale significantly, enough to match SOs from 22 onwards.
I just hoped, that Cloak + SS, Trip Mine, Fire Breath, Fire Ball, Caltrops, Fire Rain was going to be more than plenty to dispatch +2 minions. At which point im fullfilling my role in a team as minion basher. Scrappers and blappers can feed on the bosses.
Aside from Rain of Fire - which I personally dislike - looks very good.
One thing, however:
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However, with mob scaling, it seems the AoEs really get quite poor.
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I'm not sure what you mean here, I'm afraid...
Aside from that, if you're not enjoying it, don't grind away. Find a different build and have some fun! 
I think the main reason for your lack-lustre feelings Chaplain may be becuase of your lack of Buildup.
Devices still has this problem, only way around it i can see is once SO's hit, u can SO up your Targetting Drone, then Slot 2-3 recharge rather than Accuracy and try to outdamage Buildup with multiple hits rather than str8 out damage.
Shnyet AWAY
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Aside from Rain of Fire - which I personally dislike - looks very good.
One thing, however:
[ QUOTE ]
However, with mob scaling, it seems the AoEs really get quite poor.
[/ QUOTE ]
I'm not sure what you mean here, I'm afraid...
Aside from that, if you're not enjoying it, don't grind away. Find a different build and have some fun!
[/ QUOTE ]
Fight even level trolls or hellions on Cherry Hills in The Hollows. 2 AoEs slotted with training SOs is enough to kill the minions.
In Boomtown, 10 levels later, fighting vaz or council, the same 2 opening attacks do 50% damage to an even level. Even, caltrops and rain of fire struggles to finish them off.
Mob HP / resistance must scale, or we'd all be 1 shotting everything in sight with the advent of SOs. So we all look forward to SOs but its not like the villains aren't slotting up their SOs too 
Ah. Resistance increases, yes. I was thinking along the lines of the GM scaling for all levels sort of thing. Silly me. 
Well, my Fire/Dev was a big departure for me, from my norm, single target boss killing stuff.
I took Fire Ball, Fire Breath and later on, Fire Rain, which suited my team make up. (Controllers, Rad defenders etc)
Anyhoo. At lvl 18, he just doesn't cut it. Really poor. I read pre ED guides which are completely Useless now (and should be updated or removed!) which talk about 2 shotting blues in Boomtown etc. Well - ED prevents this i think. Best i can do is fire off Fire Breath, Ball, Caltrops and Rain - then run. 50% of mobs drop. Ish.
In a team im finding the AOEs very lack lustre. They are good for about 25% health on a +1 Mob. Which is common.
I was looking forward to the Trip mining goodness. However all the guides refer to the 1 shotting mines of Pre ED. Which i would have thought is not relevant anymore. And, the rate at which my team moves through the map pretty much puts Mining at the solo side of things.
I hate to lvl a character to 20ish and then find out i dont like them, so i guess im appealing for a bit of reasurance that things will get better. Just rolled an Elec/Energy and my thoughts are that at least thats usefull AoE??
How are you guys playing yours and am i missing something? Just seems very boring, with little variation in playstyle.