This study critically assesses the claim of the cartel party theory that the party in central office (PCO) has lost its powers to the party in public office (PPO) as parties have adapted to various changes in their operating ‘environment’. The study argues that a party’s tendency to adapt is conditioned by the party’s ‘genetic’ heritage: if the PCO assumed a prominent position during the party’s institutionalization, it can more likely stand against external pressures compared to a PCO that has been traditionally weak. The study compares the development (1983–2017) of two Finnish parties, which hail from polar ‘genetic’ traditions: a social democratic mass party and a conservative cadre party. The change of the party ‘environment’ has strongly supported PCO’s decay. Unlike earlier longitudinal studies on intra-party power balance, the study assesses all significant power dimensions and finds a contradictory development: while the distribution of leadership positions and resources increasingly favour the PPO in both parties, significant ‘genetic’ differences in the distribution of formal decision-making power have not diminished at all. If statutory regulations matter, the results suggest that the PPO cannot ‘insulate’ like the cartel model expects in parties where the PCO’s strong role has been strictly codified.