I also believe speed buff for Blaze (and Yenzine) should be enough and AOE for Obsidian, so that the specialized land tank is really powerful, almost as powerful as Ilshavoh (but the range still gives the Sera bot the advantage, and the raw high health that doesn't require energy to be high and boosted by veterancy). That way, the hover tank is more useful but not too powerful, and the expensive t2 unit is what you expect : strong.
However, it's not mentioned clearly, but the Obsidians also got a shield regen buff (4 hp per/sec regen instead of 2). So the question is : is the combination of these 2 buffs too strong? I don't think so, but the games / replays will tell.
IMO, since the Obsidian doesn't benefit nearly as much from veterancy as the Ilshavoh, it should have a decent shield regen speed (for reference, Harbinger regen speed is 9 hp/sec, so 4hp/sec is still not that much), not to mention the fact that the shield requires energy to run, and the unit becomes really weak without it (and in engy mod, with lots of Obsidians, it really matters). But we don't want to make Obsidians too strong so we need to keep an eye on them.