I don't understand how DDI appeared like a "necessary tool". It was not needed to build PCs, nor to build creatures.for many 'predatory' is a perfect description for 4e.
An easy example would be the direction WotC purposefully took with the PHB:
One had to purchase 2 PHBs as opposed to the usual 1 offered by other editions to get the general content required for a player and DM to utilise the combination of races and classes one preferred. Add to that the DDI subscription which appeared like a necessary tool for players and DMs alike
And my group was also able to start a 4e game using only the PHB. We didn't have to purchase 2 PHBs to utilise the combination of races and classes we preferred.
I'm not sure what the threshold is for "predatory" selling of content - but if we suppose that M:tG is something that crosses the threshold, I don't see how 4e is meant to be an instance of it.
For the sake of clarity - by your criteria Pathfinder would also be predatory in it's market model, wouldn't it, because it is also about selling a large amount of material to a given audience. (I don't really like the word "hooked" - I don't think RPGing is addictive in any relevant sense.)If 4E was WotC trying to sell as much content as they could produce to a core, limited audience, and 5E is them trying to sell a core product to as large an audience as possible, I think the more predatory approach is the first. My choice of word may not be the best for everyone, and I don't think it was a purely predatory approach...as you say, no one should be compelled to buy anything.
But given the massive amount of material produced, the subscription based service for DDI, and the practice of new content rendering old content moot (which is something I really dislike in games), it certainly seemed like WotC at that time felt they needed to wring as much money out of the folks they had hooked in order to succeed. "How do we get these X amount of people to keep spending?"
I'm also not sure what you eman by "new content rendering old content moot". The errata was all free, so I assume that's not what you mean. Are you talking about some of the instances of feat overlap with Essentials? I would say that's a pretty small component of the overall 4e content produced.
I agree that 4e and 5e have obviously different business models. And 5e's clearly seems to be superior from the commercial point of view, and also from the point of view of many D&D players. But I don't think "predation" is the right way to characterise the differences between them.