I don't know about other TCG but Splinterlands is more similar to another mobile game that I play, Clash Royale. In that game, cards balancing are done on a monthly basis. The decisions to nerf or buff a card is based on data gathered from the millions of games played daily. The key analysis is win rate at the top level. If a card in Clash Royale has higher than expected winning (or losing) rate, then it will be considered for a nerf (or buff).
The last balancing by Splinterlands was done months ago and I think it is time to look into this now. Besides looking at game statistics, players feedback is equally important too. Because monsters cards in Splinterlands are assets tradable on the market, i.e cards have value. Decision to nerf or buff a card will impact its value on the market. Some hodlers will make noise. Others will rejoice.
Some monsters that needs looking into are Prince Rennyn, Lord Ariantus, etc. If you don't have these cards, you can't compete at the very top. I do not have the statistics, but I believe Earth team will Rennyn has extreme high win rate. This is not good for the game, imo. In Clash Royale, such meta will quickly be balanced, so that the game remains fun.
I believe regular balancing of monsters cards will bring more fun to the game and add speculative activity to the cards market as well. Hope the founders and devs will take this seriously. DECs and orbs and new monsters had brought new excitement to Splinterlands, but it is now time to go back to making the game actually fun and playable again.