Yeah I kind of feel like the same, except it wasn't 14 months for me but only 6... still I love the game and play it almost every day. It's crazy how much the game evolved in the meantime and in what a good manner. The developer(s) do a decent job in managing the cards so the old ones don't become obsolete.
Here is a 99 mana battle I played (and won) but like you said, using 50 mana is quite a challenge, I don't think we will ever have cards to fill the 99 mana cap.
https://splinterlands.io/?p=battle&id=4dec01158dface3c08be93e079d2dbdf8c07ef43
I think the team has done a great job making sure the old cards are not obsolete. They made sure not to replace them with cards that were too similar, while still created the demand for the newer cards with the mana cap expansion. Often times I find it is too difficult to fill 38 mana with just the old cards, making me crave more of the Untamed cards. The same thing happens when I encounter the 12 mana cap.