If you're feeling good and running well, don't worry about it. A guy I follow on Strava qualified for and competed in the OT marathon. His 10K PR is more than 3 minutes faster than yours. His HR is usually in about the same range as yours on his easy runs. His easy runs are slightly faster than yours, but in percentage terms he's running easier (more slower than race pace) than you are.
If you're feeling good and running well, don't worry about it. A guy I follow on Strava qualified for and competed in the OT marathon. His 10K PR is more than 3 minutes faster than yours. His HR is usually in about the same range as yours on his easy runs. His easy runs are slightly faster than yours, but in percentage terms he's running easier (more slower than race pace) than you are.
I'm having the same situation at much slower speeds. I've been getting back into shape this past year. Got my mile time down to 6:00 and my easy run cannot be quicker than 12:00/mile pace basically ever. It's a weird feeling running half speed compared to mile effort but doesn't necessarily feel "off" from a mechanics perspective. Just feels like you're leaving 90% in the tank. But even then my heart rate is nearing 75% of its max.
Obviously I'm very aerobically underdeveloped but I'm hitting 85% max HR at like 9:30/mile. The speed reserve I have between that HR and my max is huge. My HR only goes up 25 more beats going from 9:30 to 6:00 pace.
It feels like the only workouts I can do are easy runs at 12:00 pace or fast intervals 800m or less. Any faster pace for any significant time and my HR is too high for too long and the fatigue will be costly. I would be doing threshold work at 9:30 pace. Maybe that's what I should be doing but it feels pointless if it's that much slower than race pace.
With all this replies and a bit of search i've found one thing called ADS (Aerobic Deficiency Syndrome) which i seem to fit all the "symptoms". Basically i have a really good anaerobic side but my aerobic threshold is really low like 5:20/km, comparing to my anaerobic 3:20/km is so spaced out.. seems like im going to have a fun weeks/months running easily to push my LT1 upfront