I think we keep coming back to the fact that an APC fits well and efficiently for certain forces... in many forces...
1. LAMI- when AA is too great or Air Power unavailable or general garrisons.
2. PAMI- Mobile command centers, duration battle recharge stations, or general garrisons.
These make up the largest portions of the SICON military arguably and thereby make allot of sense for us to have various forms of APCs, including wheeled and tracked.
The Pegasus is insufficient for APC duty aside from high speed or recon. Its open topped, vulnerable, and lightly armed, and expensive in fuel presumably. Also I doubt it can operate in high-gravity environs.
Whereas the traditional APC would avoid all this.
But I don't think we all consider that to be a 'Tank' the Tank in most people's eyes and ears is the Main Battle Tank, which we have little to no justification for in terms of fire power in the SST universe.
Marauders, Exo Suits, air bombardment, PAMI squads all have virtually the same fire power of a MBT, and superior mobility/agility, but inferior durational speed. Due to drop capsules durational speed is not usually an issue, and air drops are very easy and affordable to the federation, I would argue that air and orbital traffic is very very normal for them.
As to armor, I would wager that when faced with the mobility issue the armor issue evens out, especially against the bugs, where they could swarm a tank up closer than the tank could possibly fight back, crawl over and under every portion and tear it to pieces.
Whereas the various power suits can jump away into the air...
I think the tank lovers need to accept that a Main Battle Tank should only really come up for forces that just can't hope to have the technology of suits, such as independent non-federation colonies, or militias given antique equipment. Hardly something we need models for specifically. Such forces should be severely hampered by a lack of 'real' support from the MI.
Whereas the tank lovers can drown a little of their woe in the fact that we really should have a well developed APC with 2-3 variants for both PAMI and LAMI.