6 months is not reasonable, I doubt you can argue that sensibly.
I agree with you there - 6 months is not an acceptable timeframe. Having a small team isn't an excuse. If that's the case, then it needs to be expanded. If they can't afford or be bothered to expand it, then they've lost a potential customer: me. If others want to spend their money on their products, more power to them, but I just don't feel like spending my money on a product with bad customer service when there are better companies out there.
And this is coming from somebody who worked on a small (<10 people) warranty/production team for 3+ years on very similar products; I know what the challenges are, since I faced them every day, but our turnaround time was nowhere near 6 months.