I personally think "it sounds uninspired" is a perfectly reasonable critique to make. To imply that an artist will always be bursting at the seems with energy and creativity, especially when this is a business, is just not realistic. There will be times when the members of Dream Theater will be 100% inspired and times when they may not be. That is just human nature and is the same for every band and every artist throughout time.
For example, had Portnoy, who admittedly was tired and ready for a break been involved in the entire creative process for ADTOE, I'm guessing the lack of inspiration would have shined through in his playing.
I don't think its an insult... I think it's an acknowledgement of human nature. If something comes off as lazy songwriting to me I don't think it means "I don't like the band anymore". It just means I know they are capable of better as I have heard them make more creative choices.
With all that said, I like the new album and I'm happy they still have it in them.
Jumping off this, as you mentioned Portnoy, and the last DT album he appeared on is a good focal point of the band sounding uninspired. As much as I enjoy BC&SL, and I do think it is one of the band's better albums compared to recent work, using the word "uninspired" might be appropriate in describing the album. There are moments that make me go "well they could have worked on that transition a little more" or "his playing sounds like he's going through the motions" in regards to MP's playing, Rudess' playing, or really anyone in the band at the time. JLB's vocal melodies tend to follow what the other instruments are playing or vis versa all over the album, and the album features a 12 minute song that reprises themes from previous songs on previous albums and only includes about a minute of new material (which works in context of the larger piece, but I always wished it had more fresh meat on it.) JP even wrote a song about writer's block (Wither) and then in the aftermath of MP leaving and in context of ADTOE following it up with a very energetic album, looking back they were clearly sounding tired on BC&SL, MP for sure.. Of course, there are moments of clear inspiration on BC&SL (first half of ANTR, guitar solo in TBOT, the entirety of TCOT overall, etc...)
MM perhaps gave the band the B vitamin shot it needed, tightened up their sound, and I'd say they were inspired on ADTOE after the fall out of MP leaving, but since then they've been coasting on that wave since. Not uninspired, more coasting, dare I say, resting on their laurels on what they can do with the prog-metal sound they helped create throughout the 90s and 2000s. I think that while DT always have a plethora of ideas, it's how they construct those ideas which I feel has become uninspiring. The composing side of the band. The band sounded tired on BC&SL, but you can't tell me they weren't trying new things on that album, while keeping their core sound intact. They rarely take compositional risks anymore. Everything CAN be traced back to something they did in the past, without pointing out how they still have one foot pointed towards the future. You can have complex parts or sections of songs, you can get the fastest drummer in the world who can handle just about anything you throw at him, but in the big picture, the band has devolved into writing mostly ABABCAB song structures 9 times out of 10 whereas they were more liberal with how the song constructions went all the way up until and including ADTOE, which itself "borrowed" the adventurousness of IaW. Since they decided to "simplify" their approach on DT12, shortening the song lengths and whatnot, they have lost a step. The over-reliance on metal and less on prog that has followed the band since Systematic Chaos has not helped matters imo..
DoT and AV are a step in the right direction, and I would say AV is the most inspired they've sounded in many years, but there is a certain Je ne sais quoi that has been lacking since Portnoy's departure.