Napalm Canister is far less efficient than Incindiaries

I do not think they are, for the simple reason of delivery density.

I compared Napalm Canister to Incendiary Grenades because both are reasonably reliant on the ground-effect damage to contribute to the overall total, which is otherwise uncommon.
It was a factor I had not previously thought to include in my last post, but the Napalm Canister ground-effect lasts for 6-seconds, while the Incendiary lasts for 18.

This means that under optimal conditions, the Incendiary performs as described above, but when spammed provides only a third the damage over multiple rounds (Unless, of course, I am missing an initial 'fire-pool' damage from the blast). In the same time that other grenades deal their full damage, an Incendiary deals 8; or 20 total fire-pool damage that takes 4.5 rounds to fully deliver.
The Napalm Canister, by comparison, is spammable, with very minimal overlap between the ground-effect duration and thereby able to maintain it's efficacy for 3-in-4 rounds (2/3 without Gadgeteer, and 1/2 if the flamer turns off after the second shot), compared to 1/3 for incendiaries. Standing in the shot once and running out before the second fire-tick occurred resulted in James only taking 26 damage, with 16 taken in the first round.
Almost any other bomb or blast, by comparison, would have dealt their full damage unless I had moved prior to the detonation, and are suited to party-wide spams, as opposed to a single user.

Assuming standard combat contexts, Incendiaries and Napalm Canister are likely to generally deal less damage than other bombs because the majority of their damage requires the target to stay still in the fire - which requires a relatively accurate throw, and for the target to be effectively immobile. However, those same two factors make them strong against battles of attrition that favor the player, such as spawns with restricted spawn areas, like the Labyrinth Manticores, the Pirates on roofs, and the Gnomes on Ledges; or anywhere that abuse of door mechanics or LoS-Blockers can be used. In those conditions that the ground-effect becomes strong, the Incendiary Grenade is superior if taking three times as much time is reasonable, such as when the opponent cannot possibly attack the player.

With that in mind, I do not think Incendiaries are 'too strong' unless combined with trapped mobs or terrain exploitation. I also concede that Napalm Canister is likely more viable than I initially suggested, but still feel it is weak comparatively, as maintaining the Hybrid weapons is intensive for many forms of economy (action, attention, financial, Ability-investment, etc.), and feel that the return for the investment therein is lacking.

I also think that attempting to addess the Incindiary Grenade's strength in exploitation is ultimately impractical without fundementally reworking how persistent area damage effects work. It is strong because you can smack damage down and hide behind a corner while the damage ticks away, not due to its actual damage values. I feel that weakening Indindiary grenades would be detrimental to legitimate use and tactics, without actually adressing the situations that make them potent.

I dont agree that there is *any* content 'too old to be touched'.

That said, it is certainly a valid point that various content areas were balanced around the current paradigm, either because PCs or the spawns relied on certain effects in legitimate combat situations, and that instituting an adjustment may well require a significant review of existing dungeons.

I'm mostly concerned about the incendiary comparison because there really should be no question about whether you'd rather have 3 rounds of fire or a frag grenade and 1 round of fire. If there is then it's probably a mix of explosives being too bad and fire being too good.

Tesla Bombs, Cryo-Bombs, and Incendiaries are all the same cost and blast radius.
The main difference beyond their damage types/profiles I have noted is that incendiaries use grenade distances whereas the other two use bomb distances.

Beyond that, I support EH's statement that the weakness of Frags is that any physical blast damage is reduced by armor, which against mid to high level targets without Explosive Damage results in a significant degree of null-damage. 
With the Explosive Damage 3 investment, I can often rely that a frag will deal damage, but I only really use them in melee with myself where I can reliably assume I will take no damage personally.  Otherwise I prefer elemental bombs because armor stops being a problem factor.