you can safely reduce the recommended fees a little if you think they are too expensive.
those algorithm to predict fees are very conservatives and always overestimate
About fee estimation, Coinomi fee estimation is not overestimated, I checked fee some estimator sites now and I saw it to almost the same as Coinomi fee estimator. But, someone can still have the option to even reduce the satoshi/vbyte if he wants or wait for mempool to be less congestor for low fee.
Those estimators sites always overestimate fees as well. I have been following the mempool closely since I was working in an App with mempool data, and I have seen those websites and electrum suggesting 100 sat/byte when the mempool was empty and you could get a confirmation with 1 sat/byte
As I said, those estimators are very conservative. As nobody know when the next block is going to be mined (it could take 1minutes, 10 minutes or even 30 minutes) they overestimate fees to make sure you will get into the next block.
Even though blocktime is calculated to have an average 10minutes, a block may be found almost instantly or take even more than 30minutes (as it is hashing is completely random)