It is consensus, not the software you run decide what is bitcoin.
Actually, in bitcoin the software is the
only means to define consensus rules.
If core changed total number of coins to 42 million, would you still use core software because you want one web?
If Core did that, it would require a hard fork because it breaks consensus rules. This would split the network (or not--the fork would probably just be ignored). Consensus is defined by mutually enforced rules (via node software)...not by Core.
At what criteria do you define a new feature to be rule breaking?
When it breaks the rules, causing a network split.
Segwit soft fork demonstrated by using soft forks you can always do rule-breaking changes (like change the transaction/block format) while still not being rejected by the old clients.
Non-standard =/= breaking rules. What rules are being broken? Give an example. And then explain why a network split does not result.
That change is rule breaking thus it is a hard fork, just sold as a soft fork
Wrong. Soft forks add rules. Hard forks remove them. No consensus rules are being broken by Segwit.