I was trying to base them on the FW fluff and description, while doing something that added something new and interesting.
Hornet....not sure there is a huge difference between 1 shot at 4+ that does D3 hits, and two shots at 4+. Actually, a quick run through my head indicated the probability of a single hit is exactly the same either way. I'd pump for the D3 thing just 'cause it's a little cooler. 200 for 3 is probably right though, yes.
Lynx. From the FW price I assumed it is bigger than a standard Falcon but smaller than the new style Superheavies. So I thought a 1+ save, but not classed as a SH.
I know the FW fluff says sonic cannon, and I did look at the weapon of that name on the Phoenix. That wouldn't be a horrid option, though in effect you would have a shorter range Tempest whose shots ignore cover. However, the thing looks exactly like a Tremor cannon (GW fluff redaction at work) and I thought it would be pretty cool as a vehicle weapon. Price is TC cost + 100 for the vehicle. Seemed reasonable to me. I think the vehicle is too small for an Ordinatus class weapon personally, though I'd be interested to hear how the sonic lance works in 40K.
I did contemplate a single Pulse laser for the other variant, but tbh I figured no one would bother using it then (same firepower as the Hornet!). Exhibit A - the Cobra. Adding the Pulsar follows the above design, and I could imagine a Craftworld with a shortage of Phantoms whacking the titan class weaponry on a tank destroyer chassis. I'd rather keep the design and mess with cost....make it cool but not abusive due to points.
A compromise could be to use a single Pulse laser but extending the range to 100cm. Cost would have to come down a lot though.