*CV1 and VK have nearly identical stage structure and very similar layouts. VK has more rooms in general because of the larger storage space available on the MSX. CV2 did not have this.
You haven't played VK, if you say this, or you played it very badly. Levels in VK have very little to do with stage structure of CV1. There are tonnes of additional areas and slight differences. Sections themselves built like minimaps looped on itself. While the general layout could be similar, levels themselves are practially complete different only reminding about CV1, but not copying it alltogether.
CV2 had one big looped area, that was derived from VK's minimaps idea.
*You progress from stage to stage and cannot go back to explore previous stages in both games. VK added the need to find keys to unlock the door to the next stage in the current area. CV2 did not have this.
Castlevania 2 is adheres to the adventure exploration genre, like VK, but in different context. It took VK aproach and expanded on it, abandoning level by level structure and replacing it with giant map and several submaps, that could be counted as mini stages, if you want. Much like in VK, you need to find different items and upgrades to progress through the game. You can't access some parts of the world map, if you didn't have Blue Crystal or Red Crystal. Also, you can't progress further in the game, if you didn't have certain equipment and upgraded weapons. In short, while CV2 is quite different it uses the same logic as VK, but expands on it.
*Hidden merchants are shared between VK and CV2, even the graphics, they just don't live inside stone blocks anymore. I did for get to mention that there is one more thing VK and CV2 share and that's the Shield mechanic.
Hidden Merchants in CV2 look like monks in grey (sometimes different coloured) robes. You maybe speak about Gypsies in the CV2, but I am not sure if they use the same graphic as Merchants in VK and besides you can't buy anything from them. They just spout some useless advices. Shield Mechanic is present, that is another proove of relation between CV2 and VK.
*VK has MORE equipment, CV2 has DIFFERENT equipment. There's a difference.
This statement is nonsense. CV2 has much more weapons and equipment in the game as a whole. And idea of having multiple weapons and equipment (and ability to use them at the same time) in CV2 was certainly inspired by VK, however it was present there in much more user-friendly form.
*VK is the ONLY cv game where the player can use multiple sub-weapons "at the same time". To be specific VK has only 2 sub-weapons. The Holy Water and the Hourglass. Once you find them they are both usable. To use HW jump, and press forward. To use HG jump and press down. All other weapons in VK replace the whip. In contrast the Sub-weapons in CV2 work the same way as in CV2 except that you don't loose them when you die, but you can still only use one at a time like in CV1.
Nope.
In CV2 you can also use multiple subweapons at the same time. Use Flame Pillar, activate menu, throw Diamond or a Dagger. It maybe different from how you can use multiple subweapons in VK, but it is still works.
And there is no need to explain for me VK mechanics - few months ago I made a one life playthrough of this game and wrote a review about it. AI did the same about CV2 too.
*VK does NOT have an open world at all. There are no paths even. The stages are set up just like CV1.
VK stages set up in completely different fashion rather once that could be found in CV1. Each section is a looped minimap that is often have intricate, puzzle like design. There are still somewhat linear, but nowhere near the straightforward design of the CV1 levels.
If anything, CV2 was the very first attempt to make Castlevania more like Metroid.
Finally some logical statement. However CV2 ideas were heavily derived form VK. It is simply couldn't be argued. Too many coincidences in the design between the two games.