Yes, basically. Nothing to do with "weaker tiers", but the issue is that Arena matchmaking tries to match on raw stats, which, combined with the different scoring methods for offense and defense, creates different incentives for each side.
On offense you basically want the highest-statted team you can put together but which you can still reliably get flawless victories with. In many cases you would happily take a skill that did literally nothing but add fictitious stat points with no gameplay effect. Some characters that seem strong, like Kagero, are utterly worthless if you're aiming for a high rank, just because they have low raw stats. High-level offense teams typically include lots of armor and almost exclusively melee heroes.
Defense is very different. The matchmaking is the same, of course, but there's no ranking and no distinction between various kinds of wins. Actually, at high levels probably most defense wins are not real wins but are just the other player surrendering after losing a hero or two. And what you want is just to get at least 1 win against a sufficiently high-stat team for the season. Many people's experience with a pretty balanced defense team which resembles an effective offense team is that they're cutting it close doing this - they get only a handful of wins per season, on average, and so there's a risk of missing out on 500 feathers, plus it's just kind of a fun minigame to try to figure out how to get more defense wins. There are a couple obvious ways to do this, but some involve just going in the opposite direction of what you have to do for offense. Instead of loading a team with high stats even at the cost of some actual in-game usefulness, you load up the team with characters that have particularly high impact for their stat totals. Rather than having a balanced team that can take on all comers (to win 7 games in a row), you might choose an unbalanced team that is unfavored in most of its matchups but which crushes 10% of them (maximizing the total number of wins given that the AI is not very good). You might use a hero like Kagero. The main constraint here is that you still need to have high enough stats to get 251 points.
Nothing about this strikes me as very sinister. Like, obviously "using Kagero" is not exploiting the system, but that's basically all that's being suggested. That's just how you should be building a defense team given the matchmaking system. And your defense team will basically always be matched against players with worse rosters than you because, when you pick "advanced", the game is matching you against a higher raw stat total.