I hear what you're saying, but..
At 26, you're very much in the fountain of youth. The next 5 years a lot can change, and then from 31-36, A LOT more can change. Ryan Hall admittingly said in interviews post retirement that if he'd change anything, he'd focused more on his speed in the 5-10k realm and not been afraid of the weight room because he was chasing multiple marathons per year. Unfortunately, sounds like he was totally maxed out by 2011ish. That's where the marathon can be tricky, if you start running them competitively too young, instead of being in marathon prime as you're older (early to mid 30s), you're too taxed and the marathon just breaks you down and you're plagued with injuries. Rupp was a few months shy of 30 before his first marathon, and Mo Farah is 35?
I think there is something valuable in younger athletes (24-28) fine tuning and maximizing the speed element of their running economy before deep diving into marathons. Say what you want about NOP, but Salazaar's strategies with athletes moving up in distance is intriguing, even us hobby joggers.