Yarmolenko failed in Dortmund because the club was in transition plus he moved too late. Also had personal issues and seems like a prick anyway, talent wasn't the problem though. Felipe Anderson was way better for Lazio than for West Ham come on. Not just in terms of end product his overall game was way more explosive.
Fornals was not overly special in the way Modric wasn't early on for Spurs, similar players in style and substance. I'd have bitten your hand off after that game where he dominated Madrid in the Bernabeu and topped his performance with this goal
Not sure what you're arguing here. Do you think these players who have performed the way they did abroad are only good enough for West Ham?