While this is good I think the Hellbat needs a far more drastic change.
1. Hellbats can no longer be trained from the factory. Hellions can transform into Hellbats after researching the upgrade. The upgrade no longer requires an armory to be researched.
2. Hellbat bio-tag is removed as it is both unnecessary and silly.
3. Hellbats benefit from Infernal Pre-Igniter and have -5 damage from their current state.
Here's the explanation:
1. Part of the problem with hellbats is that they're too easy to get out. Forcing the terran to get a tech lab on the factory whilst Transformation Servos researches instead of a reactor really slows down the deadly hellbat drops. However the terran can spend the money he was going to spend on an armory on the research. This makes it easier to use hellbat openings for either bio or mech as you don't commit to that armory tech too soon.
2. The bio tag is flat out unnecessary. Hellbats already have so much HP that it can be very hard to shut them down with a reasonable amount of units. two hellbats between a geyser with a medivac can kill infinity lings ffs (and if they don't attack with the lings you go for drones since queen cant kill them fast enough anyway). they already 1v1 zlots and stalkers marines hellions and zerglings, they don't need to have infinite life. Healing should stay with bio where it belongs.
3. What is the big deal about nerfing hellbat damage vs light -5 and making them benefit from IPI? They still 2shot marines/scvs/probes/drones/zlings just like they did before... so it doesn't really poorly affect your drops to go in with -5 damage. Vs Zerg the hellbat would still 1-shot +3 armor zlings with +3 attack as long as they got +3 per upgrade. Vs Terran hellbats are primarily used for soaking up damage for your tanks so the damage should be 90% unnoticeable. Vs protoss hellbats are usually either hitting armored units (in a straight-up fight) or hitting very few zlots. If you are fight mass zlot it's pretty much an auto win for hellbat-clumping Terran because hellbats could have RF Hellion damage vs light and still win 0/0 vs 3/3/3 zlots en masse. sooooo..... the damage isn't game-breaking at all.
If you disagree with any of this, please let me know and explain why because right now I just cannot - for the life of me - figure out why the hellbat hasn't been modified yet.
To conclude, I don't see these changes to be so much "nerfs" as "modifications." Allowing faster research of the Transformation Servos would encourage Terrans to build hellions earlier gaining more map control and scouting info creating more interesting games that can still morph into deadly hellbat dropping fire-fests.