Space expansion and speed of light

I recently saw a video on gravitational waves that says that expansion of space can only be measured due to changes in speed of light as everything else that could have been used to measure the expansion has expanded too and hence the relative expansion has become zero. I feel that had space been the one to expand, we should have observed an increased speed of light. To illustrate further, say there are two points in space A and B which are $d$ distance apart. Light takes time T to get from A to B. Now A and B are stretched apart, i.e. we as observers now see an increased distance between A and B, say D but space still thinks that the distance between them is $d$ (I feel this is the part where I might have gone wrong). Since speed of light in space is constant, it still travels between A and B in time $T$, whereas we as observers will see it travelling a distance $D$ ($D>d$), in time T. Hence implying that speed of light increasd due to expansion in space. But the video on gravitational waves suggests that expansion in space slows light down. If that is the case then wouldnt it be much more intuitive to say that the distance between particles has increased due to some reason and that space has remained the same? Heres a link to the video: https://youtu.be/4GbWfNHtHRg