raghav4202 wrote:
is the sentence correctly formed ? as how is it made clear that his colleagues detest the theory ?
can it not be that the theory is rarely disregarded by them
The sentence is formed correctly.
Note the contrast "hardly new, but rarely..." This indicates that it is an old theory, but hardly... (what fits here?) Disregarded does not fit here, because if it is hardly disregarded, i.e. well considered, then there is no need to use a contrastive word such as "but." It becomes a contrast if the theory is hardly new, but rarely mentioned. Therefore, espoused fits well. Also, the meaning is not that they detest the theory, they simply ignore it.
I hope it is clear now.