particle も - Two も clauses and then です

When saying that someone or something is both this and that, is XもYもです appropriate?

彼は画家も教師もです。

I ask both for written and spoken. I feel like the copula is already a である so it should be something more akin to:

彼は画家(で)も教師でもあります。

Or something. But then that sounds formal or written-only.

As a non-beginner, this question is frankly a bit embarrassing to ask, as it's so fundamental, but I feel like it was never really specifically covered. Either that or getting used to reading more written form Japanese has messed with my expectations.

Answer

You have to use で and say 彼は画家でも教師でもあります or 彼は画家であり教師でもあります, both in written and spoken Japanese. If you want to make it shorter, you can say 彼は画家[兼]{けん}教師です.

彼は画家も教師もです is almost always ungrammatical, but in a rare unagi-sentence, it may make sense.

みんなの将来の夢について。私は将来看護師になりたいです。佐藤君はサッカー選手です。田中君は画家も教師もです。