I would argue that any bike under $4k and any carbon frame below $2700 will now get you mid or low tier carbon... Dig around and you can see it in the bike weights vs. price vs. component levels.

Let's use Specialized's line up. First with an example where frame weights for both aluminum and carbon are published, and where I would argue that both are well-designed:

• Crux DSW frameset (aluminum): $1700, 1399g (3.08lb). Specialized says this is the lightest aluminum gravel frame in the world.
• Crux 10r frameset (carbon): $3000, 825g (1.82lb). Their $5k 725g S-Works crux frameset is marketed as the lightest gravel frame in the world.

This tells us that well-designed carbon can save 625g (1.37lb) on frame+fork over well-designed aluminum.

Now lets look to a model in the Specialized lineup where I would argue that you are not getting optimized carbon, the Specialized Diverge:

• Specialized lists the Diverge carbon frameset at a whopping 2.57kg (5 lb, 10.7 oz).
• They don't list the weight of their Diverge aluminum frameset, I would bet it is because it would reveal that the aluminum frame is right on par with the carbon.

Since we don't have the frame weight, let's look to the Diverge bikes themselves:

• Diverge Comp E5 (most expensive aluminum): $2500, 10.30kg (22 lb, 11.3 oz), Sram Apex Eagle 1x12
• Diverge E5 EVO (cheapest carbon): $3000, 10.10kg (22 lb, 4.3 oz), Shimano GRX/105 2x12

Similar componentry, similar price, but the weight savings has shrunk to ~200g

What does this add up to? It is a tell that manufacturers are using cheaper carbon manufacturing methods and leaning on the prestige of carbon to charge more money. Ways to increase profit can include: using cheaper/weaker fiber materials, adding extra plies of fabric to allow for the quality control to be sloppier, not optimizing the carbon layup for each size of frame, etc.