Wellington was extremely well rated back in the day, but constant injuries have stagnated his development and hype; it should be noted he possesses quite a lot of attacking technique, as well as the physicality and tenacity of a DM
Think of him as a less robust, more technical version of Ramires. His long passing and vision can be quite strong, not to mention his shot is very powerful
And he's employed as a volante in Brazil, meaning that his defensive skills are very solid (he can be employed as a tough tackling DM or an offensive btb midfielder ala Guarin).
My primary issue with Wellington is his inconsistency with his positional awareness; some days he can be extremely effective, but in others he's frankly poor
Moreover, the injury issues are worrying, especially on a pitch as rough as the San Siro.
It was speculated that Sao Paulo were willing to loan him last season for a fee of 3 million euros, which would've entailed much less risk than an outright purchase for 7-10 million euros