Maximum power output of a single pair of MT-200 vs TO-264

Electrically interchangeable-yes , SOA wise-NO ....
with 50V rails -
- TO-3P - 40-50W (at best , 8R only)
- TO -264 - 70W
- MT-200 - 100W

I'd put my money on just the MT to exceed it's rating for 4R.
It is the only one with [email protected] It's larger slug and 2 screws
assure that it's thermal derating will also be superior.

I don't rate "best case" , like the OEM's do - above is more realistic.
Voltage has a lot to do with these ratings , a 264 with 40V rails/4R might also
do 100W.
Thermally , so does heatsink size .... a hotter device will have a degraded
spec. (Pc-Ta datasheet graph).

Have a look at Semelab's (Magnatech) range of powerhouse audio TO264s if you want really high power per device. e.g MAG 6332/9412 - - probably the highest rated commercially available types around. I don't think any MT200 types (i.e. Sanken) come anywhere near them.

I would of mentioned them , but they are about 8.5A 100ms @ 50V.
The other factor is again Pc-Ta , will the semilab 264 slug match
the heatspreading of the MT-200 one ?

I bet they are pretty close at 50V , (2sc3264 /mag6332 SOA) is nearly
the same DC/10ms.
The semelab is 2X the price.

In the long run, it boils down to keeping junction temperature safe, say not over 120C in worst case situation, to still have some extra safety margin, plus long time running close to max temp degrades the chip.

So Rth junction to case plus case to heat sink are of course big factors, you can read them straight in the datasheet, but you also need to consider the available heatsink.

As of safe area, while also a big factor, it depends on chip characteristics itself, same chip can be mounted in different case types.