What do people mean by "martial caster divide"?

I mean, I get it conceptually. Apparently people think that martial characters are much weaker than casters at higher level play. They are also complaining that martial characters are not complex and that their optimal stat distribution boxes them into only being good at hitting things.

Now I could go on a couple paragraphs on how martial characters are actually really well designed because literally every DM does 8 encounters per game day, but I don't think these guys can even read. We already have complex martial options!

1. Hexblade warlock: all you got to worry about is your charisma stat and you get a bunch of cool features to play around with.

2. swords/valor bard: hexblade a bit too selfish for you? Now you can support your allies too! Only issue is that extra attack comes at level 6 :(((

3. blade singer: want to play a tactician with a huge brain? Now you use your intelligence stat to kick ass. It's locked to elves but if you want just ask your DM and they'll probably let you use it with any race.

I just don't understand why so many people are complaining when you have great options already here.