RE: the point cost of immolators, just checked my base Marines codex, and a razorback with twin linked heavy flamers costs the same as an immolator, and doesn't have an invulnerable save, so I don't think we can really complain too much (possibly the heavy bolter option with inferno bolts is too expensive, can't comment on multimelta because it's not an option for razorbacks).
Personally I think the SM, SW and GK Razorbacks are bad comparisons to the Immolator, or at least to what it used to be.
I'd say the best Razorback to compare it to would be the Blood Angels Razorback as the Immolator used to be able to drive 12" and still fire it's heavy flamer.
The Blood Angel one costs 55pts and can change the TL-Heavy Bolters for TL-Heavy Flamers for free. It's also a Fast vehicle.
This is what the Immolator should be, the Immolator cant take las or plas cannons. It has the HFlamer, MM and HBolter options. It should by all rights have the Inferno Cannon as well as it has that in the audio book Fireborn and the Hellhound is based on the Immolator design.
If they wanted to make it a shitty Razorback then why not lower the points cost, it can't take the same weapons as a Razorback. The ability to re-roll to wound sure as hell isn't worth 25 points though as that's what you pay for it compared to a normal Razorback.
The Immolator should be a fast vehicle with allot more options, starting at 55pts with a TL-Heavy Flamer.
Then again that's just my opinion...