Energon Omega Supreme is tall and bulky but hollow. He's essentially a Mega Pretender shell for Energon Optimus. But you could easily reduce that toy down to the size of a Voyager and still maintain most of its play features.
And IMO Fort Max is more impressive than Gen. Metroplex, because Metroplex is a city for Cyberverse figures (e.g. Legion Class), whereas Fortress Maximus was designed for both smaller carded toys (re: the lift and central launcher/ramp) and larger boxed Autobot Headmaster & Targetmaster figures (re: the lateral ramps/launchers). He also has docking ports for medium sized figures (i.e. vehicles about the size of Gasket & Grommet). The mould worked really well for Car Robot/RiD with the central lift/launcher for the Spychangers and the lateral launchers for the Scout & Deluxe cars.
Making him gigantic cartoon doesn't make the Supreme Class toy any better. G1 Starscream also became massively gigantic when he absorbed the power of the Underbase, but an oversized G1 Starscream (say at the same size as Fortress Maximus) would just be sucky. There'd nothing about that toy that would really justify its size (and price).
Some height comparisons...
Gen. Metroplex: 58cm
Fortress Maximus: 55cm
Unicron: 39cm
Supreme Cheetor: 39cm
EN Omega Supreme: 37cm
G1 Scorponok: 35cm
Overlord: 34.5cm
Primus: 34cm
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