I am loathe to say too much because of spoilers, but Thomas is definitely a victim of the Golden Rule of Julian Fellowes, that a working class person who has ambitions in life beyond serving the status quo (which generally means literally being a servant, in their present position, for ever) is uppity and doomed to fail. There is also Fellowes' Corollary, in which they may be allowed to succeed if their ambition is approved of and practically supported by their appropriate social superior (see: Gwen and Sybil). This is acceptable because they are not uppity, but doing what their betters think is good for them, and they also acknowledge that they are not good enough to do anything on their own.