Strategic/corporate finance case studies

I recently started interviewing for corporate/strategic finance roles, mostly at mid-late stage tech startups. As part of the interview process, they have given case studies. 

These case are fairly similar. They ask you to create a 3-year P&L model or even a full 3-statement model but provide virtually no data or assumptions that should drive the model. Given that these are private companies, with no publicly available data (aside from money raised and estimated valuation), you end up having to make a series of assumptions. Then during the video interview where we go over the cases, they grilled me on those assumptions and how they are not in line with actuals. 

Examples of actual comments from an interview: 

Interviewer: "I don't see why you forecast 50% gross margin for the business. That is way too high." 

Me: "Well, based upon my knowledge of comparable companies and the lack of any data, I think that was reasonable assumption." 

Another company:

Interviewer: "So let's say you were working at this company when it was just a few years old and had to create a multi-year P&L forecast. How would you have come up with these quarter-over-quarter revenue growth rates? 

Me: "Well, I would have looked at actuals and since this business is a high-end retail company, it will be severely affected by seasonality, with holiday and winter quarters having a significantly higher revenue growth than the other quarters. "

Interviewer: "Ok, what if you don't have historicals." 

Me: "Well that would be a strange situation, but I would work with sales & marketing to get a sense of what their best forecasts are for the units they can sell over next several years and get an estimate of the seasonality impact." 

Interviewer: "Ok, let's say the marketing guy joined the firm at the same time as you did, and he literally has no clue about their prospects. What do you do then?" 

Me: "In that case, I would look at comps of similar high-end retail companies but make adjustments as this company is younger and in the hyper-growth phase. Thus, I think quarter-over-quarter revenue growth of triple digits % in winter holiday quarter is justified." 

In these interviews, virtually no question was asked about the model itself but rather the discussion was entirely focused on why I used certain assumptions and how they may not be in line with actuals. As someone who has created a ton of forecast models, budgets, operating models, etc., I found this bizarre, since in the real world, you can use actuals and other data points to guide the assumptions. Is this common with these types of case studies? What are they looking for? A bit frustrated with this and looking for guidance and thoughts. 

Thanks.