Nobody's ever as good as they think they are. If you close yourself off to the possibility of learning anything more, you'll always be left behind -- and it's usually at a point of being utter crap anyway, so maybe we're better off leaving those types stuck where they are 
It's damn near impossible to find a way to speak with your own voice in a language you're not familiar with. The more facility you have with the mechanics and possibilities of poetry, the more you'll be able to break rules and innovate (not just think you're breaking rules because you haven't bothered to find out what they are in the first place).
In my experience, learning the techniques and structure of form poetry never fails to improve a poet, regardless of whether they choose to write freeverse later or not. Similarly, people who only ever rhyme and never try to write a poem without that form skeleton to hold it together don't properly appreciate the difficulty of writing really good freeverse. I confess I don't understand why people who call themselves poets would ignore the possibilities offered by all different kinds of poetry -- it's like only drinking one kind of wine for the rest of your life, and that's a horrible thought
It's damn near impossible to find a way to speak with your own voice in a language you're not familiar with. The more facility you have with the mechanics and possibilities of poetry, the more you'll be able to break rules and innovate (not just think you're breaking rules because you haven't bothered to find out what they are in the first place).
In my experience, learning the techniques and structure of form poetry never fails to improve a poet, regardless of whether they choose to write freeverse later or not. Similarly, people who only ever rhyme and never try to write a poem without that form skeleton to hold it together don't properly appreciate the difficulty of writing really good freeverse. I confess I don't understand why people who call themselves poets would ignore the possibilities offered by all different kinds of poetry -- it's like only drinking one kind of wine for the rest of your life, and that's a horrible thought
It could be worse