...is less that of .than .这里 less 后为什么要加that 去掉可以吗

...is less that of .than .这里 less 后为什么要加that 去掉可以吗
but my own worry today is less that of the overwhelming problem of elemental literacy than it is of the slightly more luxurious problem of the decline in the skill even of the middle-class reader,of his unwillingness to afford those spaces of silence,those luxuries of domesticity and time and concentration,that surround the image of the classic act of reading.
这段是原句 我疑问的地方在开头
这段话的上文是
It is hardly necessary for me to cite all the evidence of the depressing state of literacy.These figures from the Department of Education are sufficient:27 million Americans cannot read at all,and a further 35 million read at a level that is less than sufficient to survive in our society.
那么 我的疑问的那个that是不是做代词呢?