So, while I see what you're saying, I already despise running and while I had my first run today all I could think about was how to not have to do it, HAHA. My pathetic run this morning was only 3 miles, and I'm pretty sure it's the longest continuous run I have done in 20+ years. If it even has a chance of a drizzle, I'm pretty sure mentally I'm going to skip it so I'm just trying to find alternatives.
Yes, that is what I typically do, actually. The problem is that where I live is totally flat, and I have a hard time getting my HR up ENOUGH while rucking. I'm sure if I get a better bag that I can load more weight in it might do the trick, but with 40lbs in the sack, 2 lb heavy hands, and 5lb ankle weights I still only get my HR up to about 125-130 which is a bit low, even at 15 minute mile. . I really don't want to jog with all that weight on, but that's about the only way I could do it currently since I don't have a good ruck sack and any more weight in the pack I use causes too much shoulder pain.
I have no desire to climb mountains, run a marathon, ride a century ride, etc. I simply don't want to suck wind walking up stairs and be prepared better for BJJ training so I'm not sure the modality matters as much as just putting in the work.
You probably went too hard on your run. If you didn't run for years or decades and run 3 miles on your first time out, you are setting yourself up for failure. I never liked running myself until I got into Maffetone, and saw it a necessary evil during my rugby years (before my Maffetone discovery). The trick is to go really easy and start very small. Note that the 180-age is only a guideline, as other said, and it's not the end of the story, which is very often forgotten. Notably,
from the man himself:
"If you are injured, have regressed or not improved in training (such as poor MAF Tests) or competition, get more than two colds, flu or other infections per year, have seasonal allergies or asthma, are overfat, are in Stage 1 or 2 of overtraining,
or if you have been inconsistent, just starting, or just getting back into training, subtract an additional 5."
I you are not used to running, 141 is likely too high for you. Your MAF HR is closer to 135, and this is a maximal HR, not the ultimate goal.
Personal story: during the summer I only do tennis. I am on a court most days to either play a match (2-3 times a week), train technique or various plays, rally, etc.., or help my daughter train. That's more than 10-12 hours a week for the whole summer of physical activity, some of which very intense. Training the daughter is in fact the toughest as she really likes to see me running. You would figure I would be in great shape, but when the tennis season finished, my first run was a very easy 2 miles, in just short of 30 minutes, and that was more than enough.
In the winter, before there is enough snow to XC ski, I use a treadmill, and currently my speed is 4.2 mph with a .5% slope. That's barely faster than walking. That gets me to about 130-135 bpm and is very comfortable. Basically, if I can run and forget that I'm running (just like you can walk and be lost in your thoughts), I have the right pace. Otherwise, it's too fast. That was my guidline last year and I got to covering 20 km XC skiing (classical) in 2 hours. I also did A+A snatches, not just running/skiing though. However, I tried really hard not to go over 135 for too long while training locomotion. That's not a world record, but that was enough to last me through my tennis season so that aerobic fitness was not the limiting factor. My goal is always to the tennis aspect be the limiting factor, not fitness.
All this to say that maybe you should give running another try at an easier pace, or maybe rucking at 125-130 bpm would be good enough. Also, eventually your Q&D will get longer, and this will also contribute to your aerobic fitness. If you're not planning on doing pure endurance events, who cares if it's not "optimal". You will improve and get to an acceptable (for you) fitness level eventually. Just like you maintain your BB lifts with 531 and don't go for a Smolov cycle. If it takes 16 weeks instead of 14 to get to a given VO2 max or whatever, it really doesn't matter. Better get there slower and enjoy it than get there earlier and hate every minute of it. If all else is really unpleasant, just a one hour fast paced walk may do the trick for now.
All this stress minimization is also important given your situation (toddlers, parents at home, ...).