"it's only logical" is a correct and usable phrase in written English.
You can use it to reinforce a point you've made or to refer to a situation that is reasonable and expected. For example: "Taking the bus instead of driving will save money and time - it's only logical."
So it's only logical that family cinema's ubiquitous, gibberish-speaking stars, the minions of "Despicable Me," now have their own theme park attraction — Despicable Me Minion Mayhem — at Universal Studios Hollywood.
It's only logical to change the committee's bill to ensure that those funds go to help victims.
Since AT&T has had a hard time boosting market share for its premium services, which cost $19.95 a month, it's only logical that the company should try to sell its service to the market where AOL doesn't dominate cost-sensitive consumers.
If we really want a Europe of tomorrow, it's only logical that people will go study in other member states".
But when so many people prostitute themselves for fame, it's only logical that a few will frequent prostitutes for it.
So to kick off its first annual convention, this group of game-show fanatics decided it was only logical that they meet here, outside the Manhattan studios of ABC's "Who Wants To Be a Millionaire".
And with ideas from some of the world's greatest thinkers floating around in the air, it was only logical that someone should create a conversation-collating installation.
So when the protest movement began in December, it was only logical that she became its treasurer.
Given all this, Lukyanov told me, it is only logical that Trump generates more enthusiasm in Moscow's political circles.
It is only logical that Russia should now demonstrate its resurgence by sparring with America again.
