Hits: When placing down the blast template, it is not uncommon to score over 10 hits on the enemy (For just ONE template). To even get 10 hits with a razordon, you'd need to roll a perfect 10 on your artillery die, and then roll 4 or better on 10 dice. In other words, you will never do it!
Wounds: Yes, the razordons will score more wounds per hit, but the salamanders will produce more hits!
Armor Saves: This one is the clincher. Salamanders' -3 armor save makes them very deadly... if you can wound it you can kill it. Meanwhile those str4 wounds produce only -1 AS, which isn't enough to make most things flinch. -3 AS compared to Razordons' -1 AS more than makes up for one point of strength.
Regen Saves: Cancelled out by Salamanders' flaming attacks. Razordons still allow regen.
Panic Tests: A whopping ONE casualty from a Sallie will cause a panic check, while for razordons you still must kill 25%. Good luck killing that many of an armored unit. Also, if there are enemy units behind your intended target, the odds are fairly good of killing at least one model from that unit and causing yet another panic check.
Stand and Shoot: Razordons are better here, sure. But why are you getting these guys charged? They skirmish and have M6 (or was it 5?). Avoiding combat shouldn't be too difficult.
Range: Razordons 12" Salamanders 2"-24" The flame template is 12" long, so you can hit anything from 2 inches to about 24 inches. If you can line up multiple units, you can ensure you will wreak havoc!
To illustrate, let's test both against T4, AS4+, regen unit. Ten hits land for each.
R: 5 wounds = 3.3 after armor saves = 1.6 after regen saves
S: 3.3 wounds = no armor saves = no regen saves = 3.3 total + panic check (unless immune)!
Hit for hit, razordons can't compete when hitting things with armor or regen. The areas where razordons excel are against things that you should be shooting blowpipes and javelins at in the first place. Terradons provide an even better solution for tackling lightly armored flankers. Just fly overhead with 4 terries dropping d3 auto-hit str 4 rocks. This has the added benefit of being just as effective against skirmishers due to the aformentioned auto-hit. Finally, the riders can each lob a poisoned javelin if you need to just finish them off. As an added benefit, terradons can contribute to the game in a much more productive manner once all of the lightly armored stuff is dead.
I think salamanders can still misfire... don't have my book here but seems like they would still.
Salamanders are our answer for armored chaos blocks, VC Grave Guard, DE infantry blocks, Regenning nurglings. Against other armies, they can make a mockery of their armored stuff and cause reliable panic checks. Just think of what they can do against brettonians!