With the soon to be released dragon level 5 and current available Pekka level 5, why not make level 4 available at TH9? Being the second to highest level for them, it kind of doesn't seem fair for TH9s considering TH8s have the same level troops. They are also the less-used troops in TH10, but they are still somewhat viable in TH9.
With the new poison spell it will be even easier than it was before to 3-star another th9.
We with th9 can 3-star other th9s easy using the right strategy for the base, and of course having good troops and heroes, so dragons lv4 as a th9 won't be necessary.
if you are having trouble 3-starring bases at your level, try GoLaLoon or GoHog, eventually check out other strategies on Youtube.