amkelley -- I've never biked during the winter months. In theory, I could put the bike on the magnetic trainer, which I've done a bit this year, but 20 minutes is about all I can manage.
Winter cross-training would need to be a mix of stationary bike and elliptical. I can tolerate 20 mins x 2.
In my 2016 example, I biked only during the summer months. And that was just an hour or two each week -- no where near the volume you often ride, and certainly not the "a lot" of cycling you've pondered. But I do usually ride as fast as possible (not objectively "fast," but "all-out" for me -- 18-20 mph).
Speaking of volume, your numbers are astounding. I've hit 70 miles (running), maybe four individual weeks in my entire life. You've been doing that, or close, consistently at age 60!
Hence, I really expected you to CRUSH your recent marathon, which you certainly did by any reasonable measure -- age-group place, AG percentage, etc. Still, I thought you'd run faster, based on your training. Maybe you're running TOO many miles? Maybe there's a persistent level of fatigue that you're not getting beyond, even with a taper? The flatness you felt in the half marathon maybe is only an exaggeration of what you're experiencing daily? (Dang, it's amazing you did that HM -- and crushed it, too, by any reasonable measure!)
Of course, I am the king of low mileage and rest days (and arguably a massive underachiever). And you're an Olympic Trials competitor, so who am I to say?! Still, I wonder what less mileage, a little more quality, some cross-training with an emphasis on strength, and a generous dose of rest days might do for your race performances?
KC -- Nice comeback in you HM, and good to get the first one under your belt. You'll know how to tackle the next one. Also, your background story makes your recent results all the more impressive. You've posted some really fine races.
racerdb -- Your current comeback is in full swing. A while back, as I've mentioned before, I read through this entire thread, and you're really an inspiration. And as impressive, to me, is your ability to make a living as a contractor with no employees or helpers!