No, those are horrible aswell. The variance in items you can get from diamont chests is absolute trash tier,
Yes, you can get get a Goram or a Sylphi but you might as easily get 1 f***ing xp cheese, it is also a waste of diamonds, with the exception of your 1st single pull and your 1st 10 pull.
The best way to spend diamonds is to buy extra stamina. The 50 50 100 100 100 aren't too bad to do daily. They help speed up your leveling process, they keep you competitive on your server and the stamina can be used to grind extra SS or items.
After you hit 90 reopening heroic stages to get extra awakening items is also a great way of spending your diamonds. The 20 50 50 options are the ones I recommend, however for collecting the "HoL 7" I would also recommend getting the 100 100 100 ones in, however this depends if you buy diamonds every now and then. Otherwise just stick to the 20 50 50 which means 5.5 fragments per day.
Last but not least and I can't believe I am going to say this, but the ancient box events are prolly another good way to spend diamonds. HOWEVER only because these heroes dont tend to end up in dia chest and are thus not available from being extremely lucky in CoF. Droprates on these guys vary a lot and I would advice only to try and get those heroes that will have a big impact in HoL or have a huge chance to change the meta in the arena, otherwise it is not worth it diamond wise.
Honorable mention: The forge... spending diamonds speeds up the process of getting stronger heroes and your can upgrade your forge faster which allows higher leves, more stats and you will have access to the 2nd and 3rd forge bonus faster then other people.
Imo any of these 4 things are a better way of spending diamonds if the alternative is CS or diamond chests.