The problem with being fixated on a set of principles that you apply regardless of circumstances is that you end up being a hostage to fortune. That's very much been the case for Amorin at United, where he's insisted on sticking with 3 at the back despite the fact their squad is ill suited to that approach. Recruitment of better suited players over the summer, such as Cunha, should see an improvement (it could hardly be worse), but some degree of flexibility from Amorin in the first place would have been preferable, and he's lucky to still be at United.
Similar story with Williams. Great fit of players to his preferred 3-4-2-1 in the National league, but insisted on attacking exclusively down the wings with us in spite of Ronald's inconsistency and having no true winger on the left. Rather than changing his approach he threw the players under the bus, which always ends in tears.
Martin could succeed with Rangers, but they will need to completely overhaul the squad. Whether he'll be given the time to get the team to play his way is another matter.