The closeups make it tough to see much of the overall effect, but I am not seeing excess seams and what I see look ok. What is wrong with the mitered edge in your opinion? Did you purchase the full slabs or by the square foot?

Your first picture is that of a laminated, not mitered, edge. The second picture looks like it needs some additional adhesive scraped off, but the mitered end isn't bad. There is an obvious stacked edge there also. The seam in your third picture is nicely done.

What is supporting the cantilever at your island please, and how deep is it?

A window, instead of a hood, at your rangetop is a serious design flaw and may be a fire hazard. Let's have a close-up picture and the manufacturer please.

Bump

3 angle island is impossible without seams. Range window is a code/safety issue. Is there a hood or ventilation? Blinds likely will melt, warp or burn, glass could break, window frame failure.

Added: range top was not installed to mfg specs. No competent building inspector would pass this.

From the photos, this does not look like a poor installation.

And I agree with @Joseph Corlett, LLC re the window over the rangetop. Per NKBA:

• Do not locate the cooking surface under an operable window.
• Window treatments above the cooking surface should not use flammable materials.

Agree about the fire hazard and that stone installation looks good to me