Its not. Its about to compare with SW max blocksize. So you can say 1.7 or 3.6 I dont care.
No, it will not. As far as computational resources go, SW 4 MB requires less than a 4 MB block size increase would. The increase with Segwit would also be gradual with adoption, which is what makes it better.
SW 4mb is only 2.1mb capacity at best, which yes only reaches 2.1 with 100% adoption of sw keys. so yes its gradual adoption.
by adoption its not about simply running a segwit node its about using segwit keys.
yes people have to move funds to segwit keys to help move to that.
so dont expect instant 2.1mb boost.. infact dont expect 2.1mb boost because not everyone will use segwit keys.
(seriously i cant believe it took you a year to atleast understand/admit that its gradual, but glad to see its finally settling in your mind how sw actually works..even if your still not fully clear in the details)
here is some finer details to help you understand.
the other 1.9mb of buffer space(total 4mb) this can be used for other features that are appended to the tail end of a transaction. such as confidential payment codes.(and yes even your overlord has pre-thought about what to do with the excess buffer weight area for things like CPC)
as for a proper consensus growth.. that to would be gradual.. not because people have to switch keys or move funds to anything fancy/different. but because pools will take safe 'testing the water' 'baby steps' with their increase of the blocksize.(just like gradual growth of 2009-2015 even with a 1mb buffer set)
take a look at the policy.h (the miners preferences)
/** Default for -blockmaxsize, which controls the maximum size of block the mining code will create **/
static const unsigned int DEFAULT_BLOCK_MAX_SIZE = 750000;
if say the node consensus was 2mb..
[consensus.h] static const unsigned int MAX_BLOCK_BASE_SIZE = 2000000;
pools will test the water with
[policy.h] static const unsigned int DEFAULT_BLOCK_MAX_SIZE = 1001000;
first and check the orphan rate. if all good they will try
[policy.h] static const unsigned int DEFAULT_BLOCK_MAX_SIZE = 1002000;
it could take a few days to grow to 2mb or a few months. depending on orphan safety rate.
the only difference is that many would prefer the sizes to be alterable at runtime and set to limits by usersettings adjusting by the node users
after reaching a network consensus.. rather than needing devs to control it and spoon feed new downloads after years of social drama to keep them as kings.
again its gradual just like bitcoin did not jump to 1mb filled blocks over night. even in 2013 we were only at 0.5mb even when we had the 1mb buffer set.
p.s. im sorry that bitcoin cant be explained to you in only one sentance. but please try taking a few extra minutes each day to read beyond your couple sentance concentration span limit. otherwise it will take you another year to slowly grasp any new feature