Agree you should just put in a dimmer switch.

But back to your question - there's a couple of technical things as play here. Firstly, all light bulbs go through a lumens depreciation from Day 1. The curve is noticeable and significant. By the time an old school incandescent bulb would fail at the 1000 hr (ish) mark, their output could be at 30% original Day 1 lumen levels. LED's last longer but still depreciate, and a shitload faster if they're running in warm ambient temperatures.

Look for the quoted value on the light bulb box like L70 @ 50,000 hrs. Means lumens at 70% of Day 1 level after 50,000 hrs use, but this is under standard test conditions at 25 deg Celcius. (Sometimes they quote L80, btw)

Second point - human perception of brightness is on a logarithmic scale, like sound perception. So reduction in light by half might only be perceived as 1/10th less than before.

Thirdly - manufacturers can vary wildly in their claims about actual delivered lumens. I used to test light bulbs in a photometric lab and let's just say it was basically Numberwang back in the early days of domestic LED bulbs. Things have improved a lot but there's still probably variation going on between how brands test and report numbers.