Lǐlùnjiā hé shíjiànzhě de shìjiǎo wǎngwǎng bùtóng.
Theorists and practitioners often have different perspectives.
Tips
grammar
家 here is the agent suffix for 'expert / professional' - same suffix in 科学家 ('scientist'), 艺术家 ('artist'), 作家 ('writer'), 音乐家 ('musician'). It originally meant 'house/family'; here it metaphorically means 'someone whose house is X-discipline'.
register
Slightly formal - written rather than colloquial. Sometimes used with a faintly pejorative edge, like English 'armchair theorist', when contrasted with 实干家 ('doer / pragmatist').
