Not a Issue with PLD, it's a issue with fitting everything into "burst meta" also PLD isn't that bad, it's suboptimal it can clear perfectly fine, These "modern raiders" you talk about, tend to make a big deal out of a job not performing as well as the others. Sure I think things about PLD could be changed, I've always liked the idea that your skill speed and spell speed were merged on PLD, I think improving some of it's defensives like cover and giving it more support is also good (Although "modern raiders" only really look at damage numbers)
Theirs also no point reworking every tank to be a burst job and making them play virtually the same, having the same bursty jobs, the issue isn't with PLD's design it's one of the very few jobs that aren't designed around 120 minutes, which again wouldn't be a issue if raid buffs weren't designed like they are now.
Being not "picked" doesn't make the job design bad it just makes it's output bad, If PLD was top damage I assure you despite how it's designed currently "modern raiders" would be picking it, because the only thing that matters to people like that is base line damage numbers and not how the job feels.
I honestly rather PLD remain "trash" and not good in comparison in raids if it means the jobs still fun, If I wanted to play a DPS burst meta job I'd go play dark knight or gunbreaker. I play Paladin because I actually feel like the job is rewarding to play and dynamic.
EDIT:
if 6.3 manages to fix PLD's burst a bit without removing its core gameplay then that's good, I want the job to be more viable just not at the sake of ruining something that is genuinely fun