Supporting feels underwhelming right now, my 0 second queue times prove it. It's not that being underleveled is the problem; it's that no champion in the game can do much while being 3~4 levels behind. It's not that levels are an overwhelming difference; it's that a bit of extra gold just does not offer a robust playstyle to a champion, support or not. Items are strictly better on more fed/farmed champions.
This thread doesn't have an answer to that problem, but rather an answer to supports' lack of popularity: Instead of extra gold, if support items give the supports extra experience then supporting would be more popular. **Right now, champion levels are the epitome of empowerment for every single champion in the game.** For example, players don't play mages mid because they're the best champions when they have extra levels; they play mages mid because mages are the type of champions that cannot do without being high-leveled. Every champion excels when they're a high level.
Every single champion in the game feels more empowered when they have more levels a lot right now, even AD carries. Levels are such a big deal towards making champions feel more robust. Of all things that can fairly be withheld from champions in the current state of the game, it cannot be levels. That is why I believe this change is a solution to their current unpopularity.