Well.. yeah.. of course a team's fifth bowler is going to need to be able to bat. Their job isn't just to bowl -- they're the fifth best bowler in the side. You asked for amazing fifth bowlers and I gave you lots of examples.
Yet being a good no. 8 batsman is something to shout about? And as per your question name the amazing No.8 batsmen and how successful were those teams?
This is just flat our not true. The only teams who haven't used a fifth bowler with any sort of regularity over the past few years are India and England - and that's down to a shortage of options more than anything. The likes of KP, Trott, Root, Woakes, Kohli, Rohit Sharma, etc. have all been used as cover.
Not that any of this deserves an answer, but. The pitches in the '50's especially in the W.I were far flatter than they are today. Secondly the pitches in the W.I today especially in Guyana, Barbados and Trinidad are slow and extremely spin friendly and that is evidenced that the top bowlers in the regional competition in the recent past (with the exception for Cummins last year) has been mainly spinners.
And how many times throughout history have we seen even the great sides struggle to do this? When was the last time you saw a moderate test team do well with a four-man attack?
But that's what makes Sobers, Kallis, Worrell, Hammond, Chappell, McCabe etc so special and valuable. There is no need to sacrifice your batting at all and all of them except for Worrell (and not so sure about McCabe's quality) were superb slippers as well, even more added value.
*sigh*
So who are the spin demons that you have produced recently.
I've just checked R. Hadlee's record. He struck at 5 wpm. Hadlee was a great bowler as we all know. Such bowlers are rare. More common are class bowlers at test level who would reasonably average 4 to 4.5 wickets a match. Do the math. A team of 4 would take around 2 - 4 fewer on average than the required 20. You need a 5th bowler to mop up the rest so your team is consistently capable of taking all 20 wickets. Quite often teams still fall short on a wpm basis even with a 5th bowler. I would argue you even need a 6th and that person should be a batsmen like Clarke who can take wickets in tests, before a side can feel confident they have the ammo to consistently bowl out teams.
The point of 5th bowlers is that they don't have to be "amazing", but they have to be able to bat top 6/7. Therefore, their bowling is a bonus, and the better it is the stronger a team can be with bowling rotations.