just spam enough pointless repetitive posts to get to legendary status?
No one would disagree with you if you would point out some by name, and quote some of their post with facts. I have seen a few too, same as you said who have been Legendary after the merit system is introduced but you can't say this for everyone. Maybe you got engaged with some of the spammers at a first impression.
Back when I first started reading, legendary status used to mean something, it meant that poster had something useful to contribute.
I wasn't there but it was true until 2016/17 if I'm correct as at the beginning of 2018, merit system was introduced.
Now it just means they merited themselves with an alt or they bought sMErits online and they spammed the forum enough times.
Not really possible. If someone abuses merit with a huge amount, it will definitely be noticed. And it's not that easy to buy merit I think as it has risk involved both financially and getting tagged if noticed.
Take it easy. Ignore people who spam in your eyes.