Strongly agree. Cos spoilers much!
Having said that, because a lot of toys are packaged in robot mode these days, I find it a bit annoying if I need to find a YouTube video when working out a difficult transformation (most recently did this for MP Convoy ver 3.0), and reviewers start it from alt mode and then transform to robot mode. Even in some of those "Just transform it" videos. I can understand it in reviews because you don't want to ruin the surprise, but if you're making a video to explicitly showcase how to transform a toy and not review it, then I think it makes sense to start in the order of which the toy is packaged in. There are a few videos that show you how to transform the toy both ways - but I had to search through a few videos before I found one that did that for MP Convoy - and it's not as simple as reading the video title. I'd click on each video then "scan" by moving my mouse cursor along the progress bar to see if the video shows transformation from robot to alt before then searching again and repeating the process.
Also, there are a small handful of exceptions where I'm glad the toy was packaged in robot mode, but these are toys that have fantasy alt modes rather than realistic ones. One example is Siege Omega Supreme. I avoided watching or reading any reviews of this toy before I got mine, and I'm so glad that I did because I was very delighted to discover that his forearms don't separately disconnect and reconnect to form the rocket! I was pleasantly surprised to find out that this toy has minimal partsforming! I feel that this would not have been as much of a surprise if the toy had been packaged in rocket base mode. But ultimately it's really about savouring the surprise and not having the first experience of marvelling a good toy's design and engineering being spoiled for you. Because it'd be as silly as say watching a Star Wars movie where the opening text crawl just tells you a major plot point that you didn't already know! <wry.laughter>