Not wanting to enter in an argument that seems to have got silly to me, but wanting to add relevant info for the sake of other readers. Basically stating explicitly and drawing together points scattered through the thread.
This band is not art, it's business. Players are doing it for the money, the objective is to earn the pay in the minimum time. Rehearsal is a cost (either because the players are giving up unpaid time plus or someone is paying them, plus cost of rehearsal room). Plus they may hate the music.
A lot of opportunities come because a band has a hole, and they phone around and someone says "call this guy". You get a gig, if it works you get more. Maybe the OP did better than he thought first time round, maybe he turned it around with his phone call, or maybe the other band was stuck. Doesn't matter, he got the opportunity, he knows he can do better and he will make the most of it.
To succeed in this you need the ability to fake it and wing it. Some players are better than this than others, and people have all sorts of different ways of handling it (good ear, encyclopaedic knowledge of songs, large collection of fake books and charts, etc). They know how to look confident and cover their mistakes. If you are young and want to make a living in music, you should think about how to develop this skill.
So my benchmark for "hard" is a phone call "We need you at the pub and onstage in 90 minutes. We'll call the songs. No charts, no advanced vetting of the song list, just keep up". Done it, not great at it but I know players who can kill it. They usually have great memory, perfect pitch, an outstanding ear for chords, ability to read other players, and an uncanny feel for where music is going. They make above-average money because they have above-average skills.
By comparison, 90 songs in six weeks @ 15 minutes per song to do a cheat sheet is less than 23 hours work. Over six weeks that's less than four hours a week, not a lot. Many simple pop songs you should be able to listen to the song and write the cheat sheet out as you go, like taking dictation. Put the songs in a playlist on your iPod and you should be able to rehearse them all multiple times if needed as well.
To be honest, if you can't do that and you want to make a living long-term, you have work to do. Not being able to learn quickly enough is a skill deficit, the same as not being able to play fast enough, or project an image on stage.
YMMV but that's my experience.