Holy fire currently is quite weak when compared to meta builds, although its popularity.
With 8154 hp at my current level of 86, it does 949 damage per tick. With 61% fire damage, 24% fire damage penetration, 32% burn chance, 104% burn damage, 44% magic skill damage, 9% skill damage, 12%fire dot, 25% damage percent, 10% area damage. Plus iron will support which is giving a further 191/5 = 38% and 21% magic skill damage, fire penetration giving 14.4% pen, shred giving 30% resistance shred, and flame strike giving 10% more. With all of this it does a measly 14k-15k dps.
Which is not enough for the amount of investment put in. When a full build is just around making a single skill strong, and it is still laughably weak, something isn't working correctly.
It definitely needs a buff, it is the damage skill of crusader and without it crusader is nothing more than a buff and enabler class. Immolation is weak and cant be used with holy fire cuz itd be a dps down no matter what, but it is extremely good with totems. Fist of judgement is weak because the damage is less than what other classes can do in a cast or 2 casts, but it has a 10 second cooldown. Commeupance is decent. Persecutory is just bad. Flail is a good utility for grouping. Shield throw is a good utility for increasing damage.
Holy fire tries to be righteous fire but just can't due to how bad the dps is. With full investment u can get it to do decent damage, but at that point it should be doing something much higher than it actually is.
My advice on buffing it and what has been suggested before is making it scale from 33/11 health to damage ratio, to 77/33 damage ratio the more points you put into the skill. Why is this better than a straight buff for all ranks? Makes the skill still manageable and fun to play with. It adds a layer of having to think if you can sustain the extra damage with the extra point in it, while not bricking the early early game for the skill.