First, where I live, a tube Marshall is 900 - 1400 euro, I paid mine 700 second hand almost unused. A Mesa Rectifier, around 2000 euro. Mesas sound more refined, of course they do, you are comparing semi-budget equipment with high end.
Other than that, in my opinion, this is another example of using an amp without first getting to know it.
My fellow guitar player in the band uses a Marshall DSL100 (borrowed from me), and I use a 3 channel Dual Recto.
If I turn my Presence higher than 10 o'clock on channel 3 Modern, it sounds fizzy, a bit thin and harsh. No problem at all with other settings, and simply keeping the Presence low makes it sound fat and creamy.
Playing my Les Paul on my Mesa also requires careful tweaking: a big sounding guitar through a big, aggressive amp is sometimes too much of all frequencies, also the ones that sound unpleasant. Not so with my more neutral sounding Mayones Setius (something in between a superstrat and a PRS).
The Marshall has similar quirks: dial in too much treble on the Ultra Gain channel, and it has this squeaky overly trebly sound. Simply turning down the Treble and turning up the Mids makes it sound much more pleasing to the ear. Again, no problem at all on the Classic Gain settings.
A warmer sounding cab also makes a world of difference, the same with the guitar. My buddy uses a Jackson superstrat, which he MUST replace as soon as possible. Good shred guitar, but doesn't play well with the Marshall, sounds too thin. A Les Paul on the other hand... instant creamy Marshall leads without much tweakage, in contrast with the Recto! Mind you that it is not the refined Mesa sound, it always has this grinding Marshall thing going on, love it or hate it. It's not a jazz/fusion amp, it's a rock amp.
So I have observed a similar things between two radically different amplifiers: an aggressive setting should be tweaked with care to make it sound pleasing and musical, and tends to amplify unpleasing characteristics of your other components in the chain such as your guitar.
What is really good about the Marshall is that lead playing is much more fluent than on the Recto, I guess because of the more pronounced high-mids and harmonics. It does sound smaller and boxier than the Recto, so it is not as good in creating a big wall of sound rhythm sound. It also needs more volume than the Recto to sound good (I guess the poweramp plays a bigger role in shaping the tone in the Marshall). We balance a bit by me using a 2x12 and my buddy a 4x12.
When uninformed people plug into our amps and crank the bass and treble and cut the mids, yes, both amplifiers sound horrible. The Recto even worse. Sometimes even we are not really pleased with our tone. But we've also had days were I was playing chunky riffs and the Marshall was soloing and we were floored by the tone. So my opinion is that tube Marshalls are decent rock gigging machines that can be had cheap. If you want a bigger, more refined, but similar tone there is always Orange, the Mesa Stiletto, Bogner... Where I live, this means digging out a LOT more cash (which is worth it for me).
In the end, the Mesa sounds like an amp of twice the cash, and that's exactly what it is in Europe. That doesn't mean the Marshall sounds bad if dialed in by someone with a good ear for tone and used with other decent gear. But, I must admit, as a gear slut I am trying to convince my buddy to get himself something more high end to get that 1% better tone for the band
