Miners can never force full nodes to accept anything invalid.
Right. But can full nodes force miners to reject anything? If not then what full nodes think is valid or not doesn't effect the blockchain.
Contra what you say, in Segwit, there is no witness block. Segwit witness data is included inside the same block as the rest of the transaction data. Signatures are always present. This is the whole point of segwit, so that the signature is not needed in the blockchain. False. You have not even the slightest idea of what Segwit is, or how Segwit works; youre just spouting off nonsense which you evidently make up on the spot.
If this is so then why not just hash the signatures into the transaction? Then it would be the same as we have now yet it would be a block size increase to 4mb. Segwit signatures are not hashed into the UTXO transaction and thus cannot be verified via traditional means. As far as I understand segwit is done to save space in the UTXO.