This sounds eerily like the voice of reason, have you spoken to my wife by any chance? This is good to hear though, why I like the input on this thread - having an objective view on things can keep people honest and probably help them veer towards caution and hopefully avoid injury.
A lot of what you say resonates with me. Your view on 3 week cycle of intervals/sessions is pretty much how I try and play it too. My PB was 1.25 a couple years back, this was taken after a period of 3/4 months running average 50km a week but with WAYYY too much intensity, resulting in the niggling achilles tendonopathy that I'm still feeling to this day. I ran that PB effort in what was high end tempo HR pace and left it feeling that I could definitely go faster, but because I'd thoroughly fucked myself by rushing the buildup I was never able to prove that theory (and running that pace currently is certainly not a tempo effort!)
I picked up running again in the New Year, building towards now doing about 30km a week with one interval session that is a mixture of the things you described. Doing a fair bit of cycling in between but the massive focus has been on increasing mileage/intensity slowly, maintaining strength work and trying my hardest not to get injured again (so far so good...) - the 'long run' so far is up to about 14km and all running is Z1/2 slow plodding at 70% max HR except for the 20 mins or so intensity within the weekly session. I read "80/20 running" by Matt Fitzgerald some time ago and enjoyed it, and have tried to structure my training since then around these principles. When I've pushed it I have managed a 5km just shy of 19min (with difficulty), to give you an idea of current fitness (not great).
Plan was to continue working in this way until end of May. It should mean my weekly mileage will be around the 40km mark and I'll have (hopefully) achieved a fair bit of low HR running for 4 months, giving me a reasonable but by no means spectacular base. Between now and then I intended to start drip-feeding some speed indurance reps within my long run, e.g. starting with 2 sets of 1km at HM pace and building it weekly (slowly) from there. At the end of May a 12 week cycle would begin where weekly mileage continues to build, along with some more focus on HM specific workouts.
But to be honest I am very happy to be talked out of this plan, because the main goal is to stay injury free and enjoy running/riding 5/6 days a week. I set a goal at the start of the year to run 1000km in 2021, so I could prove to myself that I can consistently run without getting crocked. Its not a massive target by a lot of people's standards, but perhaps I should just stick to that goal and then reassess at this time next year. I could possibly modify my approach and target a fast 10km this summer? Maybe I'd be less likely to get injured that way, but to be honest I think it could also work out badly because I figure a lot of the intervals for targeting a 10km would be much more Z4/5 oriented and its when i start regularly doing paces below 3:50 that my achilles seems to flare up. That's where my reaction to the 10k plan that was posted upthread stems from. Speed endurance/tempo runs at goal HM pace feel less dangerous in a way.
I welcome any thoughts/criticisms - sorry for the long post!