Easy runs and heart rate as an extremely mid miler

I feel you dude. I’m a 4:49 guy and my heart rate is always high on easy runs, I average 8:20 to get 150 hr. It’s mostly a strength thing. I would guess even the smallest of hills can cause the highest spikes in hr. If your hr goes above your easy zone don’t be afraid to fall back and run your own pace. Definitely do leg day(s) I’m the gym over the summer.

I should mention, go mainly by feel. The watch is a guidance tool and should be treated as such.

Are those numbers coming from an optical HRM or a chest strap? The latter is much more accurate, the former not so much.

My suggestion: Stop looking at your heart rate. The number on your watch isn't telling you anything useful. Find more knowledgeable people to get training advice from. The people who talk about heart rate zones are not the people you should be listening to right now.

How many miles a week do you run?

If you aren't running many miles, then you probably aren't all that aerobically developed, and so an easy run will still be somewhat of an effort.

Your mile time suggests anaerobic talent, but that doesn't necessarily translate to longer distances.

Run your easy runs easy, regardless of the pace. If that means you need to slow to 9:00 miles to keep your HR below 150bpm, then so be it.

This will allow you to run more. And as you run more, you'll find that your HR will begin to drop on these easy runs, and the pace will gradually quicken.

^^ this. The more miles you run OP the more you heart rate should come down on easy days. Stretch those 3-4 mile runs into 6-7 mile runs. Your easy days are meant to be easy so try to keep them easy. If the heart rate is high running easy then that's not a green light to increase speed. You might naturally still be seeing 160s @ 8:00 pace but that'll come down.

Those numbers are from a Garmin HRM strap

You are probably right, I only run 20-25 miles every week. This summer I’m looking to increase my mileage a bunch for a better base

Try to keep her under 160. Lower to mid Zone 3 is totally fine if you’re not putting in a ton of mileage and you’re still working on building a good aerobic base.

Ive made the habit of changing my watch display to just show heart rate on my easy runs, some days I’ll be hitting 7:00 miles keeping it under 150 bpm and some days I run high 7s or low 8s to keep it under 150. Strava has created the nasty habit in us of worrying about pace on easy days when it really does not matter. Are 7:00 miles training your legs to run 4:40 pace in a mile or 4:10 pace in an 800m any better than 8:00 or 9:00 miles? No. But those 8:00+ miles still train your heart and lungs which is the purpose of easy/recovery runs without beating your legs up as much. The biggest mistake I made as a highschooler was thinking 6:30 miles on easy days was something to brag about.