まだしも

まだしも says the first case would be bearable, so that the second, the one that actually happened, stands out as too much: "X would be one thing, but Y". The bearable case comes first with なら or は, and the complaint follows.

The first half is not praise. It is only less bad, and the speaker's annoyance or disbelief lands on the second half.

ならまだしも and はまだしも

ならまだしも makes the first half hypothetical, "if it were X". It is the form a verb or an adjective takes, and the ば-form does the same job. はまだしも sets two real things side by side: X is acceptable, Y is not.

まだしも belongs to writing and careful speech. In conversation, ならいいけど carries the same complaint: いち1じかん時間ならいいけど、さん3じかん時間はひどい。