The only thing that would prevent me from going that route is that the risk is much higher on Lamar/Kyler than Mahomes. With my first round pick I want to minimize risk because I can find upside later and risk early really hurts if that risk happens. Plus Mahomes still has the high ceiling potential so you aren't losing too much there either.
I thought of your reasoning when picking mine and was going to point the average finishes of Jackson and Murray in either median points per game (a stat that is posited as being stickier than avg PPG per I forget who on Twitter) or rank-ordered finish the past two years under the aforementioned scoring standards, but didn't have an effective resource off the top of my head.
I think Jackson was by far number one in 2019 for 4 pt passing TD leagues. He was eighth or ninth last year in a six point passing TD league last year, so it's not like you're missing out on an expected top twelve guy by taking him, especially in the 4 pt. format, because I think that he had a clear below average year last year compared to what we can expect. But that's my personal take on Jackson. I think last year was, if not his floor (that's too extreme given he missed no games to injury), then at least a year where we saw a downturn in production that will have been an aberration for him.
But I think I'm with you on sticking with Mahomes. It's just, to be honest, I don't like his supporting cast anymore. I don't care for CEH and I don't like that they have Kelce, Hill, and nobody else to really speak of. So the other guys (Jackson and Murray) and their rushing dynamism creep up in there.
One last thing: I didn't list Josh Allen because he's rushing TD dependent for his overall rushing points and I expect him to regress in the number of goal line and inside-the-five touches he keeps for himself. I think Moss will eat into that, even though they were largely by design. I think they'll call for less punishment up there in Buffalo. Can't have him getting hurt. Jackson's the same in that he can't get hurt, but that's another story altogether as his running is more integral to his game, even more so than Allen. Murray has already said this off-season that he'd like to scramble less this year, but we'll see about that. Edmonds and Conner are not likely to be workhouse backs that siphon off Murray's carries. Edmonds's size and Conner's looking bad from injury might not give the Cardinals that luxury.