The devs don’t know how to adapt the gp ranking system to these modes.
Let’s consider guardian first. Like all other modes, players would have to be awarded gp for elims. However, in guardian elims would be very easy to farm simply by camping and defending the leader. This means players would be incentivized to farm kills instead of hunting down or killing the opposing team’s leader. Farming would be rampant because players would know exactly how much gp they need to accrue in order to rank up the fastest, and the nature of guardian allows rounds to be extended for a very long time. This would especially be the case in one-sided matches. Furthermore, leaders would be incentivized to chase elims for gp instead of playing smartly. This is because in very long rounds the leader would miss out on most of the gp from elims if they are playing smartly and avoiding risky or unnecessary combat. Since TC would likely cap elims, at best everyone would hit max elims every game and the only factor differentiating players on the same team would be gp from leader kills and/or surviving as leader.
This is not ideal compared to the previous ranking system which likely implemented numerous factors behind the scenes including duration survived as leader, duration of rounds, duration of match, kills as leader, leader kills, damage dealt on leader, rounds won vs lost, composite ranks of opposing team, penalties for deaths as leader, penalties for deaths/downtime, etc. Not to mention, in the previous ranking system players would receive score based on damage dealt so real kills far outweighed elims in terms of performance. One might say that farming kills was an issue in guardian even before this ranking system was introduced and I would say that I agree; it was a factor that held back the ranked guardian experience because players would play for kills instead of playing objective. However, the gp system (with caps) would significantly magnify this issue because players would know exactly what targets to reach in order to boost their ranks up as fast as possible, actively encouraging them to farm. The problem is the gp system does not allow for very much nuance because complete transparency requires oversimplification of how players rank up.
Now let’s take a look at escalation. A good escalation player would never double cap rings because the ring caps at the same speed regardless of how many players are inside of it, so one player could leave to be positioned ideally for the team. If gp is awarded for capping rings, then ranked players would multicap rings for gp. Same concept for breaks (esca rings don’t break instantly). Furthermore, if gp is only awarded for caps, breaks, and elims then there would be little penalty for deaths or low uptime despite these factors playing a huge role in who wins rounds and matches. Lastly, players would be incentivized to chase elims for gp instead of positioning correctly to win rounds. These issues existed to some extent with the previous ranking system, but for reasons similar to those I outlined for guardian, the transparent and oversimplified gp ranking system would exponentiate them.
So there you have it. If you want these modes back in ranked like I do then I would suggest proposing a viable way to adapt the gp ranking system to them, because sadly there is a very low chance that TC will ever revert the ranking system.