Having a lower kick number means that the fire becomes a bigger problem sooner. If it was something like 5 or 6, two sprays of chem will handle it completely (although if it's just at 8, a single spray of chem will handle it right now too). Fire extinguisher is just for bigger stacks of fire. So when it reaches the kick point now, it's a big problem in both being kicked, and the damage the stacks are doing. Or something like that.
Ultimately lowering the kick stacks won't do all that much. Nor will strengthening fire. The real issue is the effectiveness of chem spray and fire ext. Personally I like how they were improved, but it did impact the effects of fire in a big way.
There's almost always someone chem spraying on a ship, especially if they see you going fire heavy. It's very difficult to get any stacks of fire going on anything but guns (they usually just keep the core components sprayed), and those are easy enough to deal with since everything else is fire proof.
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Some ways to work around the infinite chem spray is to break components. Once something breaks, the chem spray buff is gone. And once they rebuild it, you can easily get tons of fire stacks on it before they try to chem spray it. Of course if this tactic takes off, they'll be better about chem spraying instead of smacking it with a mallet first thing when it's rebuilt. There's always the problem of breaking it before you set fire to it, as that's kind of the role fire should be doing, and why bother at that point? Really it's nice for the balloon or engines, as the breaking and fire stacks will keep them off the hull long enough for the chem spray to wear off, at which point the fire can do it's thing all over the ship.
So you can still do fire heavy builds, you just can't rely solely on fire.
If there was something to adjust to make fire just a smidgen better, it'd probably be with the fire fighting tools; although it would have to be a very delicate change.