Ah I might have to disagree on that part.
Season 1 pacing was perfect. It allowed proper development of characters and the story progressed really well which made an impact.
But there were quite many subplots in final episode alone which could've easily filled up two more episodes.
For example, I didn't really like how Zaun vs Piltover's decades long conflict got immediately resolved by Jayce's simple speech.
And Sevika got completely sidelined in Act 3. She barely got any dialogues, but was elected into the Union Council without any explanation.
Things like these could've been properly delved into if we had some more episodes