Training Suggestions

I'm mainly running so I'm using only running suggestions and they are quite well balanced for me. I assume you have calculated HR zones for running, so maybe the watch does not have enough data about your running to give you reasonable training suggestions. The pace you provided in min/km or min/mile? For min/km it looks reasonable for a fit runner, but yeah min/mile is absolutely hardcore :)) 

it's /km ;-) So quite slow. But 20 minutes 2 min/km less than average is hardcore for me. And sprint, even for 15 sec. with 3 min/km less too

Have you tried calculating your running lactate threshold with the watch? Sub-Threshold (used for this 20 minute run) is moderately hard pace, not 'struggling-for-every-second-of-breathing' pace, so perhaps calculating the LT will solve the issue for you. All you need to do is a dedicated ~20 minute running workout. Here is how to run the test:

https://www8.garmin.com/manuals/webhelp/GUID-31D23DBB-57C2-4DF7-A0C9-8D1A00AB4BE7/EN-US/GUID-1B0C9B93-01CD-4A0C-A30F-B815C0347159.html

Generally 20 minutes in threshold is pretty ok - my threshold is ~2minutes less than my marathon pace (aka. super comfy long run pace), so maybe the 3 minutes is an overkill, but I'm no running coach ;) 

3kkman said:

But 20 minutes 2 min/km less than average is hardcore for me. And sprint, even for 15 sec. with 3 min/km less too

I do not see anything like that in the suggested workouts you listed in the OP  :

3kkman said:

(typical pace of 6:15, intervals of 15 seconds at 3:20 or 20 minutes threshold at 4:30).

However, do not bother about it too much. Do it in the best way you can, without suffering too much, and without injuring yourself. The workouts are adaptive. My suggested workouts were too slow at the beginning, but because I struggled to keep the slow pace, the next time I already had a faster workout. And it certainly works in the opposite way too.

As kidney_thief wrote, you are probably better in biking, and the suggested workouts are based on your fitness level from the cycling. The watch is learning about you with each run, so you just need to continue running, and the workouts will progressively adapt to your true running level.