The Dillon BL550 is not more complicated than the T7, it's just different, while at the same time being more versatile. The difference between the two is that instead of a rotating toollhead, the 550 has a fixed toolhead with 4 die positions, and a rotating manual indexing shell plate. The shell plate only turns if you want it to.
Both presses can be used as a single stage press and both presses can be used as a turret press. The difference is that the 550 can also be used as a progressive press, while the T7 cannot.
So you could use the 550 as a single stage at first as you learn, then when you're ready (like in the future) go to progressive mode to significantly speed things up with the addition of a case eject upgrade. The T7 will simply never be able to match the speed of a 550.
The 550 also has the advantage of having virtually no flex, so it's ideal for loading match grade ammo.
The only downside to the 550 is that .308 and .300wm use different shell plates, so you would need an appropriate conversion kit for each cartridge. Changing them out would take about 2 or 3 minutes, so not long. The tool heads are swappable so the dies can be left in the tool head, then the whole tool head changed when needed, That takes about 15 seconds. You would need a total of 2 tool heads for those 2 cartridges.
I hope this clears some things up for you.