I think direct accountability is overrated. Not to say that it shouldn't be there, but I don't think it's important enough that the electoral system should be fixated on it as the primary goal. For example, in US today, despite single-member districts (which put it as the cornerstone), party politics dominate in practice.
I think MMP is a reasonable compromise system between direct accountability and regional representation on one hand, and proportional representation of national politics on the other - each district still gets a direct representative (or several; I'm not opposed to multimember districts in general), but party lists are used to keep the overall balance of power in line with the national vote.
The risk with the system that you describe is that it can still skew results substantially. For example, a party that consistently gets just under 20% of the vote across all districts would end up with no seats at all, although 20% is a significant proportion of the population, and in fairness is entitled to appropriate representation. This can be improved by adding more members per district, but then the legislature becomes unwieldy - in fact I would dare say it would be unwieldy even at 5 members per district in US, since it would push the number of representatives over 2000. Increasing district sizes proportionally would mitigate that, but it also decreases the connection between the elected representative and the people in their district, and thus also accountability.
I think MMP is a reasonable compromise system between direct accountability and regional representation on one hand, and proportional representation of national politics on the other - each district still gets a direct representative (or several; I'm not opposed to multimember districts in general), but party lists are used to keep the overall balance of power in line with the national vote.
The risk with the system that you describe is that it can still skew results substantially. For example, a party that consistently gets just under 20% of the vote across all districts would end up with no seats at all, although 20% is a significant proportion of the population, and in fairness is entitled to appropriate representation. This can be improved by adding more members per district, but then the legislature becomes unwieldy - in fact I would dare say it would be unwieldy even at 5 members per district in US, since it would push the number of representatives over 2000. Increasing district sizes proportionally would mitigate that, but it also decreases the connection between the elected representative and the people in their district, and thus also accountability.