A couple of points I would like to make both for and against this issue. As a preface let me say that I am for wards and vision in the game.
Riot has said that they would like to decrease decision fatigue players experience especially when there is an option that is strictly better.
As this applies to sight stone, in almost every single pro-game of league in every region sight stone was bought. This implies that not buying a sight stone is such a high cost that the decision isn't the players to make, yet the player still has to make the decision to buy it or not. The main advantage that period had was when to buy the item prioritizing early damage or early vision control. Riot has removed the decision of whether or not to buy vision. Now the matter of a players choice is whether to try to roam to help other lanes with ganks or to stay in lane and try to get your wards faster. The cost benefit of these decisions is you might get your mid ahead, they end laning stage early and roam around the map. (which adds vision for your team) If the gank doesn't go well you have traded off guaranteed vision from the quest early for a chance to get vision possibly earlier.
Riot also said, as was stated, that one of the reasons of the decision for wards to be connected to support items while removing the non-ward variant was to increase supports item diversity. Over several years this has both succeeded and failed depending on which factors you look at. If we once again look at pro-games from the time period years ago, season 5 is the example I will give, almost every game
(Aegis of the legion) was bought by the support player. So in their 6 item slots, 1 gold income, 2 boots, 3 sight stone, 4 aegis of legion, 2 slots for choices. (not given in order items were bought, also the sight stone item could condense with gold income item for less slots but that was a decision) Now supports have more open slots to work with, 1 gold/wards, 2 boots, 4 slots for choices. As a whole supports still are not allowed to choose every item, a fail for their reason, but supports do get a lot more diversity, a success for their reason.
Being able to buy vision was an important part of the game, it said as a player/team 'I think information is more important than stats'. As we have seen time and time again over the years that information IS more important than stats in most cases. When you can work as a team communication, is information, when we buy wards, is information, when we ping, that's information. Information is powerful. One time or another we have all been stomped by a team of players that had better communication with one another. Before league added voice chat using another program to communicate with your team was a strict advantage outside the control of the game. One of the problems with the ability to buy wards is until you learn that lesson of how powerful communication and information is, as a player you will be outclassed by those until you prioritized information where appropriate.
On the note of information and smart decisions, lets talk about the current state of vision in lanes in regards to junglers. When you do not have vision and do not have your jungler on the same side of the map you are suppose to play 'smart' play passive and respect that the other jungler may be near. This leads to less kills, safe play, and 'boring' play, which according to riot they are trying to get rid of playing too safe. Having more vision as a whole means you can be more risky when you have it. With the most recent changes to towers and the bounty system they are trying to balance this safe, smart playstyle by enticing you to take more risks while ahead or behind. If you are behind you get more gold if that risky play pays off. While ahead you get more gold if you try to be risky and push your advantage on them and their tower, that has a limited time offer.
TL;DR
Many of the mechanics and decisions that were present with buying wards and sight stones are still there in regards to top tier play, though they have a different face. I do want more vision and wards in game. I want other players to be able to invest in vision in more meaningful ways than a control ward.