Slow progression is to be expected in a F2P game. They have to entice you to buy stuff. You can't compare it is previous Halos, CoD, or any other pay-to-play shooter where the PvP is a driver of game sales. In Halo Infinite, the multiplayer exists solely on mtx. So, you know for sure they're gonna work you for money constantly.
That's a serious change for Halo. I'm concerned about how it will impact PvP in the long-term.