Heat Lance Idea, someone run the numbers please.

So had an idea to toy with the Heat lance and make it worth those 25 points. Strength, AP, Damage and special abilities are maintained as current. The differences are: Range 24". This makes it top tier range for melta weapons. Alteration 2: replace Assault 1 with Rapid Fire 1.
So, you have a scary damgerous gun with good strength and near-matchless AP and damage for an infantry weapon, while having enough shots to threaten vehicles and big monsters at close range while stomping multi wound infantry into the ground.

Can someone run the numbers and see how this compares to the blaster for various roles point for point?

Assuming a 3+ save and the weapon bought by scourges (for point cost considerations)
The problem is not that the melta is never better. The melta sucks because it needs to be close enough to be in melta range which put's you at more risk. And the preferential targets are very very rare compared to the t7 tanks. Give it rapid fire and suddenly the dark lance is still better at everything but t5 and t9-11 at long range, but in rapid fire (and melta range) the melta suddenly is much better. Thus it actually becomes worthwile to get in melta range.

Let's just look at the basics in melta range first.
T5 and lower the melta wins (although not much units have that many wounds a t5 no invunerable)
T6 Melta wins, but with very little difference
T7 Dark lance wins Big
T8 Dark lance wins but only a small difference
T9-11 Melta wins

It might be good for hunting centurions.

Honestly giving it range 19" would be enough to make that weapon work.
The only thing that matter right now is : you can't DS in melta range, making it useless for 50% of the units that can take that weapon (well, a talos technically can, but who does that ?).
Making a melta weapon rapid fire would be... ballzy.