I think burn helps somehow but Its all about that token or the coin which is gonna burn. It depends on that altcoin's quality, market demand and manay thing. Burn won't help you team burn a shitcoins cause it has no demand. And how a token could pump if nobody willing to buy that token? But if it comes to potential altcoin, price will pump after announcement of burning. Cause it doesn't matter how burn mechanism work but people will crazy buy that potential altcoin which could be reason behind pump. Something influencers also promote and do burning announcement for pumping token thus way.
some shitcoin devs could be burning 99% of their total supply and it won't change a thing because its a shitcoin that doesn't have demand but its different if its ethereum that burns 50% of its total supply the value would be instantly doubled, thats the thing with burning, it requires the coin to be at least having sufficient demands first before it actually can works.
as of now, I rarely see some devs burning coins though I don't know why it was massive marketing strategy back then when many shitcoin was still a thing and get invested heavily, the devs trying to make this sense of scarcity that could make people eager to invest in their shitcoin but later on losing so many of its value.
in a nutshell, its not really a effective marketing strategy anymore.