I'm saying playing any of the instruments in rock band would fundamentally help with rhythm assuming OP has none since he said he's having trouble with beats yo
Rock Band has the added benefit of having multiple styles of music packed onto a single disc so you can get your shoes wet in different melodic styles but that's tangential to what I think is more important
I don't know any music theory and I don't think you need any to make a good song. Having a good rhythm section is more important IMO and then your banging melodies supplement it. You can teach yourself rhythm if it doesn't come naturally, and you need it, even if you're making mario at a rave music. If you're having trouble making beats I suggest going back to basics.
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Good luck OP don't follow my advice because it actually is pretty bad
EDIT: but seriously it's real bad never listen to my advice seriously how much of this was sarcasm and how much was truthiness I'm sorry I promise to never shitpost again until I inevitably shitpost again