What can you tell me about Marcus Almeida "Buchecha" ?

[Einheri]

Ah, for me he should be a 4th degree or a 5th degree...

No. 13 years at black belt is long enough to be a 3rd degree black belt. Degrees on black belt represent a minimum time in grade. When you actually get the degree depends on when you're given it. Some people stay at a degree for a long time because they either don't care or don't have a connexion to anyone who could award it them. It is not skill based in Jiu-Jitsu; black belt is the last grade received on skill-based merit, after that it is just time served.

And why are there a lot of grappler who climb the degrees and get higher and higher degrees?

Simply because they served their time in grade, and were promoted.

 

[Coconutwater]

It's honestly meaningless

To me, a jiu jitsu black belt who fought at least three mma fights and won at least two of them, should already be a 2nd or 3rd degree, especially with today’s competiton.

 

[Emanuele]

To me, a jiu jitsu black belt who fought at least three mma fights and won at least two of them, should already be a 2nd or 3rd degree, especially with today’s competiton.

Promotions isn't based on MMA but on BJJ competition resume; I can be 6th degree and never been a MMA fighter.
Btw it would have been interesting a grappling match between him (Almeida) and sambo player Artem Osipenko, in 2019, inside an MMA cage, Almeida in gi and Osipenko in kurtka and sambo shoes.
Back in 2019, Almeida was a pure BJJ player and Osipenko a pure sambo player; both were in their prime, both almost same age, same height, same weight, same experience, same resume. A grappling match, inside an octagon cage, with Almeida fighting with BJJ and Osipenko fighting with sambo, it would have been a great event, IMHO, even greater than MMA matches.

 

[Einheri]

To me, a jiu jitsu black belt who fought at least three mma fights and won at least two of them, should already be a 2nd or 3rd degree, especially with today’s competiton.

Degrees on a Jiu-Jitsu black belt represent time spent as a black belt. That's it. Black belt is the last merit-based grade you get.