Instead of waiting each season, let's have a half-annual gameplay shuffle.

One of the biggest things that makes the meta fresh is massive gameplay changes. People can't stand having one champion dominate meta without a setback for more than 15 patches. Then again, people who like seeing that champion make light enjoy and begin to focus on making the most of the power streak they have.

Direct nerfs harm the people who play that champion, especially if they're a popular champion. Direct buffs to older champions makes them into a 1 or nothing gimmick champion ( Think Shaco ) who can wiggle their way into playing with the popular champions.

So why not focus on "reworking" things they use most?

Here's a good / bad example of when this helped / harmed a champion.

Dark Harvest went from a stacking auto-attack rune, which only champions with auto-attack resets ran; to a execution rune which is better than Electrocute if you can takedown many targets. That hyper-buffed Evelynn, allowing her not to shy away from champions she couldn't E. However this made the rune more rare to see on a champion like Nasus, who only used it because of the auto attack empowerment.

Stormrazor was probably one of the most controversial items in League since old Morollomicon. An item with a large price tag on it, not the best stats for the amount of cash thrown into it. But a promised 1 crit made a ton of champions reveal themselves. Probably one of the worst cases of this item being overtuned was on Caitlyn, who could now instantly kill whomever steps in her trap and extend her rapid fire combo ( Crit -> w -> e -> passive aa ) by one as well as Jhin going into godspeed mode on-hit. But this allowed some champions like Riven and Gangplank to show some amazing potential.

These meta-breaking adjustments keep the game fresh unlike direct buffs and nerfs. Imagine if the rune which reduced your damage early by 15% but gave you 500 bonus health afterwards came back, wouldn't a few low-listers make it awfully high?