I think what Tim Cook said was that for SOME people, who don't need all the features of a full desktop OS, the iPad Pro would suffice. And for SOME people who use a laptop at work or in meetings, but don't need the features of a full OS, the Pro could substitute for the laptop. Regardless of what he really said, it is clear that the Pro is not a laptop. Attacking it for not being a laptop is a straw man argument. If you want a laptop, buy a laptop. If you really need a hybrid, buy an MS Surface, and you'll see why a hybrid gives you the worst of both worlds: a sub-standard laptop and a sub-standard tablet.
... we have an iPad in every possible size and I don't think it's necessary...
YOU don't think it's necessary to have three sizes of tablets. That is a valid opinion. But it's just your opinion. In my opinion, it's very necessary to have three sizes of tablet because different people have different needs. I am finding that in my own personal, subjective experience the iPad Pro TOTALLY outshines the iPad Air for several kinds of activities. So far, I've found that viewing streaming media, reading web sites, viewing pictures, reading a magazine, and playing pinball are WAY nicer on the Pro than on the Air. And the speakers are really nice when viewing video. OTOH, playing chess and cards are actually easier on the Air, since those do not benefit from the large screen. And it's worth noting that at 67 years old, my eyes are not what they used to be. Younger people may not have the same experience, but that does not invalidate the usefulness of the Pro for a significant part of the population. Remember, you are not the only customer. Clearly, the Pro would be a poor choice for you, but for plenty of others it is ideal, and that means that it most definitely is a necessary addition to Apple's line-up.
And FWIW, the iPad Mini is a marvelous device for people who want something portable and easy to carry, but for whom a phone is too small. The Mini is lightweight for travel, and easy to hold for reading a book, yet still large enough to view a web site and type on the on-screen keyboard. Not as great for viewing web sites, or as easy to type on than an iPad Air, but much easier for both than a phone. And the light weight makes up for the shortcomings, for people who want something easy to carry.
All three sizes have their ideal uses, and their markets.
The Pro has a smaller market due to its cost, but it's far and away the best in its class and some people will find it the ideal tablet.
People who don't like it are entitled to their views. But it's just silly to say that it will be a failure because you don't like it, or because it lacks the features you want