Was SegWit implemented with consensus?

Bitcoin Mechanic explains that SegWit was added to BTC despite the concerns and disagreement of big blockers.

No. SegWit was never implemented with consensus. "Consensus" means that everyone agrees, but during the Blocksize War the SegWit upgrade was added to BTC using a soft-fork which the big blocker/BCH community rejected with a chain split. This is sometimes used to generally demonize the BCH community, many years later, as people who could not "respect consensus" or who somehow didn't understand how Bitcoin works. Neither of those things is true. If anything, the implementation of SegWit was disrespectful of consensus given the enormous controversy surrounding it at the time.

The existence of BCH is proof on its face that a large section of the Bitcoin community disagreed with SegWit and the community was not in consensus for its implementation. If everyone had agreed, there would never be a chain split at all, let alone one with a thriving community nearly a decade later. This is before even factoring in all the censorship and propaganda implemented to stamp down opposition.

Contrast this with the 2021 Taproot soft-fork upgrade to BTC. No chain splits emerged from that, as everyone involved agreed with it - it had consensus.

Partially as a result of this experience, the BCH community later developed the CHIP process to upgrade without splits. The BTC community still has no explicit upgrade process.

Some other important notes:

SegWit was NOT a blocksize increase, although it created more transaction capacity and allows larger blocks.
The BCH community fixed transaction malleability WITHOUT SegWit, so there is no technical barrier to a BCH Lightning Network. SegWit was never needed to fix transaction malleability.
SegWit specifically is a part of dispute over the real Bitcoin among Bitcoin purists.