Three mana for an any-color source is the floor, and that floor matters in a format where the splashy payoffs (the colorless indestructible top-end, a third-color legendary bomb) reward reaching past your two main colors. The home is goodstuff two-color midrange that wants to land something off a splash without warping its mana. P1P6 to P1P8 there, lower in mono-paired aggressive decks that get nothing from the fixing and would rather have a body on three.
The two activated modes fork the evaluation, and the skeptical read holds. Nothing else in TMT feeds the counters, so they accrue at the rate of your land drops. Escape Tunnel does better than most, since it enters and then sacrifices for a basic, banking two triggers in a single card rather than one, but that is marginal acceleration on an already slow clock. The ramp mode wants two land drops banked before it pays, and two colorless on turn four or five doesn't move a midrange game much by the time it arrives.
The three-counter mode is the honest sell, and the reason is the type line. Grounded for Life and Stomped by the Foot both read "target creature," so the format's bread-and-butter removal can't answer Weather Maker at all; it sits on the board and accrues triggers where a creature would be killed first. By the time you have three counters, the 2/3 and 3/2 commons are still the relevant targets, and 3 damage clears all of them. A removal-resistant, repeatable source of creature kill is a real rate, just a slow one competing with the ramp for the same counter pool.
Maindeck in anything splashing a third color; left in the pool otherwise.

