I try to do that too, play each game as its own. But in this case, it's supposed to be a spiritual successor, so comparing it to its predecessor is 100% valid in my eyes. But I see where you are coming from

I only played D3 for a month before D2R released and I never looked back, so I can't honestly compare a game I'm currently playing with a game I haven't played in years, not in such minute detail. But comparison's to previous games are not necessary to determine how much stash is needed in D4. The whole design is wrong for the intent.

You have 10 character slots for those 4 pages of space. Most people won't use them all and most who do will have hc sc and season characters which all have separate stashes so one can assume 2 to 4 characters per mode as an average. For 1 character (in sc), 4 pages is well more than enough. In hc it's still more than enough even if you keep stuff in case of dying. No matter how many builds you'd like to be able to try on a whim, it's quite sufficient. Even with holding onto every type of gem.
2 characters in sc is about the same, but if you want to have all the builds available well now you're out of space. In hc you'll have to start choosing carefully what you want to keep.
3 or more and shit starts going completely off the rails.

Now this isn't an issue for everyone. Maybe not even the majority. Most people I know only have 2 or 3 characters. Though all those people are feeling the stash space issue. And the game's still young.
However, it was part of the development strategy to make it fairly easy to respec to a different build, and that flies directly in the face of such a limited stash. Just making the 1st page of the stash akin to D2 and locked to the character would have been enough to handle all 10 characters in a single game mode. A tab specific to aspects would have a similar effect. 4 pages of shared is just not enough. 10+ items per build, 10+ aspects to hold onto in case of equipment upgrades so you don't lose power when acquiring new equipment or have to let the equipment sit in your stash until you find the aspect desired. 20-30 slots per build per character. So you cannot just respec to a different build on a whim, despite that being the intent during development.

There are other aspects of the game that could have mitigated the issues to a degree. Having equipment levels correspond to item power instead of character level when dropped would allow for multiple characters to use the same equipment much more easily, which would reduce the need to have multiple pieces of similar equipment in your stash. A separate page for gems, and a more developed codex where you can replace dungeon aspects with equipment derived aspects (or not replace but just for storing) would have a huge impact.

There's a lot of stuff they just glossed over which most would have seen issues with.

Well said.

Did we just have a conversation that ended in respecting each other's views?

Dear god, what is happening