Segwit spending transactions, Segwit spending payments, and payments and blocksize charts can elaborate Segwit adoption and unused Bitcoin block capacity.
So unused Bitcoin block capacity is the reason average is still around 1.7MB despite Segwit increase adoption to legacy.
SegWit is not something separate to not be considered. It is part of the protocol and witnesses are part of transactions so they are part of the blocks and are contributing to the size.
Okay I think I understand what you meant by Segwit not been separate from the traditional Blocksize.
Size is measured in weight and Segwit is 'lighter' than Legacy
So 4MB of Segwit is 1MB of legacy. Traditional limit wasn't changed
Segwit just made it possible to have 4MB in place of the 1MB because of it's 'lightness'