I think this might be mostly because Senators and Congresspeople are basically like the old aristocrats, each dragging behind them a train of assistants and policy analysts that are working directly for them, serving as the technocratic backstop to their policy decisions. A short-term congressman necessarily will have inexperienced employees (at least, inexperienced in the considerations of that particular district), and thus—even with the very good normative beliefs (the things that are "their stance")—they will have flawed positive beliefs (their knowledge of facts and research that can inform "their stance.")
If you could truly split congress from its technocratic base, such that each new member of the House or Senate is just "plugged in" to a long-lived technocratic base-infrastructure (in the same way the President is!) then we could achieve much shorter term-limits while still achieving high effectiveness.
We could achieve shorter term limits, but if the problem is persisting political opinions that may not represent the people, then it may make the problem worse. :/
If you could truly split congress from its technocratic base, such that each new member of the House or Senate is just "plugged in" to a long-lived technocratic base-infrastructure (in the same way the President is!) then we could achieve much shorter term-limits while still achieving high effectiveness.