The best aluminium frame manufacturers have abandoned 7005 like Giant and Merida a while ago. Their entry level aluminium frames tend to be 6061 now and use 6066 (Merida) and 6011 (Giant) for their premium aluminium frames. I don't think fuji-ta the world's biggest high quality aluminium frame manufacturer uses 7005 now or if it does its for specialist orders, they use 6069 for their premium frames. Lastly I remember reading on alibaba a factory that stated it now made high quality aluminium frames of 6061 and had stopped making inferior 7005. On face value 7005 is stronger but 6061 allows easier hydroforming and shaping of the frame so can more easily localise in the frame strength and flexing to improve it's overall performance. I believe 7005 tends to be more brittle and fatigue more. It naturally air hardens over time faster making it more brittle even without use. 7005 can have a higher strength to weight ratio but beyond that I think most of the positives belong to 6061.

I think with Giant who are the actual manufacturer of their own frames you can be sure that as the prices goes up the frame is improved but for many brands where the company is a importer from the far east and may use different factories depending on which gives the best price then its more difficult to judge quality by price. Such brands do not have consistent quality in my opinion. Some importers used to use Giant aluminium frames (probably the best) but have started using other factories for cost reasons. The 2 top aluminium frame manufacturers Giant and Merida have lost a lot of oem orders to cheaper taiwanese companies who manufacture outside Taiwan or mainland China manufacturers (fuji-ta etc). Trying to spot the real manufacturer of frames can be really difficult. Cannondale is easy as 6069 is a fuji-ta premium aluminium and the fuji-ta site clearly states they make Cannondales as well as many other brands of Dorel; GT, Schwinn etc. I think they have a long term relationship. Other brands may have manufacturer's tender for contracts and then you don't really know who makes the frames as there could be multiple suppliers. When Tern had all their frame recalls it was clear they were using multiple factories not just for different models but for batches of the same model. So different owners of the same bicycle model and same year can have different quality frames. For me if I'm buying some bargain end of year hugely discounted bike I'm not going to be too critical but if I'm paying top money I would at least want to get a brand that actually manufactures their own bikes.

Lastly if you ever spend the time to wander around a large bicycle retailer looking at bikes purely from a quality perspective; paint finish, weld beading, component choices etc it's often easy to find bikes that stand out as appalling value among the average value or good value bikes. It can even be from the same brand that offers good value bikes elsewhere in the shop. Sometimes you see children's versions of bikes also available in adult sizes and everything has been downgraded to light duty parts but the price remains surprisingly close to that of the adult bike despite obviously costing a small fraction to make with its limited gears, freewheel and more basic unbutted frame. I'm just making the point that brands are more than happy to exploit customer's brand perception to maximise their profit and margin and its not always related to what it costs to make.