In my opinion, there are places where butyl rubber is the ultimate choice and others where it simply isn't appropriate. Take this image for example, which crudely shows two cross-sections:
In the first case butyl rubber will work amazingly well at sealing two parallel, flat objects.
In the second case it might work, but not as well as a sealant designed specifically for perpendicular sealing. This is the case for the windows in my bus. As the windows are tightened from the inside of the bus, the window frame tightens against the metal support, which is perpendicular to the frame. If butyl rubber tape were to be pressed onto the window frame before tightening, it would get sliced in half by the support. Some may stay in between and keep things sealed, but a thermoplastic sealant will work better. Also, you wouldn't want to use something like automotive seam sealer since it doesn't cure. It stays sloppy, collects dirt and can easily be morphed.
You'll have to look at how your windows are installed to determine which will work better.