Game balance must take first place,reality should be second.
And giving firebugs the axe is the best way to rebalance them? Rather than, say, making their strengths worthwhile strengths on higher difficulties, you'll just remove their weaknesses instead?
I always see firebugs IRL as people who stand near the front line of a camping spot. They shouldn't be moving around fast, because they carry a lot of heavy kit. But encouraging people to kill scrakes and FPs like a zerker, and with the fast movement speed of zeds on HoE making the DoT damage nearly useless, you'll be encouraging people to make them zerker v2.0.
Anyways, with a full set of equipment and no movement speed buff, they still won't be able to kite fleshpounds like a zerker because they'll be too slow. And no, they are not having a speed buff as well.