My problem with the altars is the fact that they're "permanent"; if one side captures both altars, it's more or less a permanent buff for that team until the other team manages to steal back an altar. However, if the team with the buff is very good and coordinated, they'll snowball out of control and make it almost impossible for the other team to steal it back.
I have 2 possible suggestions for this. First, make the altar buffs timed. After around 2~3 minutes, make them go back to being neutral. I'm not sure whether to have a separate timer for both or to extend the timer, but either way, it will help leash the "permanent" buff problem.
Another idea is to change how the buff is applied; make only one character that captures an altar get the buff. This should also include some balancing of how much buff is received, for both the individual and for the team.
The downside to both of these is the fact that it may make the altars too much of a focal point of the game, instead of laning, ganking, and team fighting in general. However, it may bring more strategy and options for players, like deciding when to go for the altar or who should get the buff.
I know it's not a perfect idea, but this should hopefully bridge the gap between the previous TT players who want the old monster buff system and the new altar system.