Even when the congregation is tired, the source says:
• do not omit Salawat in each Tashahhud;
• do not omit the opening Thana;
• do not omit the Ruku and Sujud Tasbihs.
If people are weary, the optional dua may be omitted.
Shorten where the source allows shortening, but preserve the Sunnah elements it specifically tells the prayer leader not to remove.