I bought a 1966 blackface Fender Bassman amp in 1966. It was a 50-watt all-tube amp and it was great back in 1966. Was fine for high school dances and playing in college. Then in 1971 I started touring with a nightclub band playing 5-nights a week, 50-weeks a year for 3 years. It worked fine for about 3 to 4-months. Then the keyboard and guitarist both got Vox Super Beatle amps and drowned me right out. Their amps were 125-watts RMS. So I then traded in my Fender Bassman amp and bought a Standel amp that was more than I needed anywhere.
I would say that you will find the 50-watt amp head weighs a lot and doesn't deliver that much. It will
not be an upgrade from your Rumble 200. It will be a sideways move at best and really a move down from your current amp. It will work fine as long as you don't have a loud drummer, guitarist, or keyboard player. But speaking from experience with a 50-watt Fender Bassman head, it won't hold up if they go anywhere near 100-watts.
If you really want tube, then check out the Ampeg V4b, 100-watt amp (weighs 41 pounds - yes tube heads are heavy). Street price looks like, $1,299. Or check out the Fender 100T all-tube 100-watt tube amp weighing in at 48½-lbs. for a street price of $1,499. And by the way, those may not be loud enough for large venues.
RE: Bluesbreaker head - as you noted that is a guitar head. The amp they based thier whole series on was originally the 1959 Bassman 410 with the open back speaker cab. That cab shredded speakers in short order when used with a bass, but quickly became a guitarist favorite. The entire bass breaker series is based on bass amps that guitar players loved...just say no. Would also be terribly ironic to buy a guitar amp that came about because it was a poor bass amp, just so you could use a guitar amp as an imitation of a bass amp. Just wrong on too many levels...