The Cremator is more like an auto grenade launcher than a flamer and it's ammo type is energy despite being a flame ball shooter in theory and the non explosive and some explosive perks apply

Like the flamer, the Cremator deals fire damage and applies a burning effect to its targets. Unlike the flamer, the Cremator lobs explosive fireballs, applies its burning effect to enemies within the fireball's explosion, and consumes 10 fuel per shot. Furthermore, the burning effect is large, dealing 50 fire damage a second for 6 seconds at base, and can be increased to 80 fire damage a second for 12 seconds with the slow burning mod. This damage over time effect scales with additive damage bonuses like Heavy Gunner perks, Adrenal Reaction and the Junkie's legendary effect.

For the actual weapon I would recommend getting not only the cremator but all of its mods from the season pass and that includes Multishot, napalm, and longer burn as all of them greatly increase the damage output by default

well for starters let's list them together

For more damage: you need all three of the heavy gunner perks and Demolition Expert in strength

for bigger blast in perception: you need grenadier so you can increase the blast of each shot up to 100%

for Intelligence I would recommend: batteries included and gunsmith and to top that off I would say stabilized to get more armor penetration

for other special perks they include:
Bullet Shield
Lock and Load
One Gun Army
Bear Arms
Bloody Mess
and maybe Covert Operative if you also use sneak

Yes there are two that can decently help you considering on your playstyle

Follow Through and Far-Flung Fireworks both help with the cremator shots

Master, expert or normal heavy gunner: increases damage with non explosive heavy weapons (still works with the cremator

Grenadier: increases the size of the explosion from the fireballs

demolition expert: increases the damage of the impact of the fire balls (the extra damage doesn't show as being there but it is)

batteries included: allows the weight of your fuel to be next to nothing which allows you to carry about 50k without any real weight

gunsmith and weapon artisan: makes your cremators durability drain slower and you can repair it to 200% of its durability

stabilized: makes the actual balls the cremator shoots have armor penetration

bullet shield: give you damage resistance while shooting

lock and load: makes you reload the cremator faster

one gun one army: gives up to 12% stagger chance and a 12% chance to cripple a limb

bear arms: makes the cremator weigh less

Bloody mess: gives up to 20% damage boost on the condition your target might explode into well nothing

covert operative: gives mroe damage on a successful sneak attack

The Two legendary perks
Follow through: gives more damage on ranged shots when sneaking
Far flung fireworks: chance to make targets explode dealing heavy damage to nearby enemies with a chance of a chain reaction happening

Thanks for reading my guide and Finally NO bethesda is not going to nerf this nor are any of these bugs it is a seasonal weapon only available right now meaning that it was meant to be this way