Except arguably the pyromancer upgrades scorching burst so that it is just as good as the other options. I don't see the problem, personally.
If by "arguably" you mean "at level 10". I find it telling that a heroic pyromancer is still quite likely going to want freezing burst over scorching burst. +1 damage is not very special.
So, and now we look at 'Scorching Burst' and 'Freezing Burst'. Both are fully the same, but Freeze is 'cold' and also slides...
That tells us either that fire suck for effects or the 'fire' damage type itself is considered better than cold.
BTW, Freezing Burst neither slows, nor targets Reflex.
So it is ok for an at-will to be just weaker than others, because there is a specialized build (Pyromancer) that benefits more from it's damage type?
But using frost-cheese (lasting frost combo) isn't good enough and available for everyone, so Freezing Burst can be better.
Still not convinced their is a rational for the weak Scorching burst besides they avoid errata in this case.
You sure wouldn't... if you're playing a pyromancer.Except arguably the pyromancer upgrades scorching burst so that it is just as good as the other options. I don't see the problem, personally.
Neither is a 1 square slide, frankly. Pyromancer wouldn't be the first build ever to not really come into its own until later levels.
In any case that's what specialization does. You get the benefits of specialization, and they're offset by narrower choice.
If a power is underpowered, it probably won't see play. So, unless it's something a character is forced to take, it's not in PRESSING need of errata, since it won't be a problem in play. And, if it's only RELATIVELY underpowered ... like say any non-twin strike at-will for the ranger ... there is probably not as big of a problem. Yes, the cold burst power is better than the fire power, but is scorching burst worthless? Not necessarily. There is no reason to pick it over the cold one UNLESS you want fire damage (for pyromancy, or you know you will be fighting trolls, etc) but if you did pick the power, it's not like your character is necessarily going to be gimped.
Now that Flaming Staffs don't work, I'd argue pyromancers are "forced" to take Scorching Burst.
Plus, the shear fact it exists as it does means the wizard will never see another multitarget fire at-will, since that niche is already filled. There's no hope of them replacing it with a better different power.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.