The whistleblower protections are an important tool to keep government responsible, and I'd hope we can all agree that it shouldn't be abused for political purposes. The concern is that it may have been abused here. I think the interest in this "whistleblower" is three-fold:
1) Did he have first hand knowledge of this phone call or did he hear of it second hand - why was he told about it if he wasn't primarily involved? If not primarily involved, who told him about the call, and was that legal? His original claims about the call were pretty outrageous and don't match the released transcript. Was this a coordinated "resist" effort by political opponents?
2) To contine point 1, was this primarily politically motivated on his part? Reports are he was a previous adviser to VP Biden and close and active political supporter of Biden and Clinton. If true, it further calls into question his motives and accuracy/honesty.
3). Did he coordinate with Rep. Schiff or his staff prior to submission - did they help write it? Not only does that call into question the legality of the complaint, but it also contradicts Schiff's statements, and if true, many fair minded people would conclude this was a political stitch-up.
There are probably other concerns, but these are the three I'm tracking.