I agree with your take on the success rate of mid pricers, and am going closer to GnR myself this year than normal (like for like), partly as a result of this.
With that said, I think the success rate of mid pricers is much higher when they're fallen premiums than when they're speculative breakout type players.
Subject to fitness, I'll say Smith and Steven. Smith has 3 of his last 6 seasons at 89+, most of it before he started playing more mid. Steven has 6 of his last 8 seasons at that level, with three of them 103+. They've obviously had injury issues, but Steven was actually very durable until this year, and Smith is only 26, and I think broke the tackles and pressure records in 2018.
Whitfield is a gun player but I think the risk/reward of starting him could be skewed to the downside. He hasn't been at elite level for long, and I reckon players tend to have a softer patch after they reach that level (through a reversion in form, attention, etc). GWS should also have more mids available this year, so perhaps there could be some impact to his role? Might not be huge, but he looks more like an upgrade target to me.
The other thing is that's forward rookies are generally weak, with a shallow pool. The X vs Y probably includes about the 4th or 5th best forward rookie (we will already have #1, 2 and 3 regardless) so if it's like earlier years, it could even be a struggle to find someone who will play the first six weeks or so with any confidence.
I agree with your take generally, but in the circumstances I'm inclined to err the other way.