I will not speak to the rest of your assessment of Ariete AMV vs Leclerc since I do not have Arietes. I felt comfortable addressing the DM53 aspect since I have plenty of DM53 shooters and also own the Leclercs.
I enjoy my Leclercs even though they have some issues and I in no way think they are second worst. I feel they have a lot of average/good aspects and no real, clear stand out strength. However, the combination of these aspects make it a good tank, especially in high end players’ hands.
My opinion only (as an average at best player…I find top end players can make any tank work, so…)
The dart: it is average at best and struggles to kill in a single shot which paired with the Leclerc’s armor and 3-man crew can spell trouble. The round is obviously not as forgiving as the DM53 or US top round and a few others. That is no big deal to elite players, but for a potato like me it matters.
The optics: very good, but Challys, Merkavas, and others also have very good optics
Gun handling: very good (the closest to a standout area), but again a few other tanks have equal handling so not a definitive it is the best in this area to set it apart
Mobility: Very good. The ZTZ-99A, WZ, Abrams, and others are agile as well, so even if the Ledclerc is slightly more agile, it still does not stand out
Armor: It is okay-ish, most armor cannot stand up at top tier anyway, but I feel the 3-man crew paired with the armor hurts it a bit more than 4-man crewed tanks. It definitely does not survive shots like the BVM, Leopards, STRVs, or even on occasion the Merks
Reload: this became less special after recent buffs. Do not get me wrong the 5 sec autoloaded gun is good, but many people at least expert their crews and get their reloads very close to 5 seconds without having the risk of only 3 crew.
Fellow French players: this can be a huge strength and no matter the cause (lack of high tier premium, forum reputation of French tree, etc), many French line players are very good. I forget the streamer, I think Semicooperative, but he had a great point about passive and active advantages of tanks. He said that the Abrams and Leclercs have more active advantages so the tank really shows in the hands of good players, but can appear weaker in the hands of an average or worse player. As I said earlier, the elite players can make any tank work. Just for completeness, the streamer identified the survivability of things like the BVM as passive strengths that allow the average to below average player to survive things they usually would not in a more active advantage vehicle. I think this is quite true.
When you combine all the factors together, I find the Leclerc to be an average tank (in school grades I would say it is a B- maybe for an average player, but probably an A for an elite player like most tanks would be). I personally think tanks in game should be looked at from an average player perspective not the top or bottom folks.
As a parallel to how I rate the Leclerc, I personally love the Chally’s in concept, but to me they are closer to a C- or D when you aggregate the round (2E, BN) and the mobility (3TD, BN) with the huge breech weak point and other armor weakness.
Anyway, just the thoughts of a mediocre (at best, on a good night) player.
An addendum: I also think that the differences between most of these tanks matter far less and cause me far fewer deaths than CAS killing me from afar with little to no defense. Just had to throw that in there ;)