All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
The method of praying the Witr prayer which you described in the question is that of the Hanafi school of Fiqh, which is one of the Sunni Schools of Fiqh followed by many Muslims.
The Hanafi scholars held that this method is permissible based on some statements of the Companions. Hence, you may imitate them and follow the congregation of the masjid. You should not do something on your own whereas the people in the community where you live do something else as long as there is probable evidence for it and a notable imaam is doing it.
As regards the method which you suggested in your question – which is to sit down for the Tashahhud in conformity with the imaam without reciting it in order to avoid making the Witr prayer resemble the Maghrib prayer – then this does not benefit you, because just sitting after two units of prayer makes the Witr prayer like the Maghrib prayer in its form, even if you do not recite the Tashahhud.
You should know that according to the view of the majority of the scholars, it is not forbidden to make the Witr prayer resemble the Maghrib prayer; rather, this is only disliked. The Shaafi'i scholars said, “Likening the Witr prayer to the Maghrib prayer is disliked.” The Hanbali scholars said, “It is not disliked, but Al-Qaadhi Abu Ya’la forbade this method.”
Ibn Taymiyyah said that the person has the choice between the two methods.
We advise you to follow your imaam and not leave until he leaves so that you get the reward of praying with the imaam until he finishes the prayer, because a person who prays with the imaam until he [the latter] finishes will get the reward of standing in prayer for the whole night. Also, not conforming with your imaam might lead to Fitnah (tribulation), disputes, and corruption of the hearts. In this regard, Shaykh Ibn Taymiyyah said:
“It is also permissible to abandon what is better in order to soften the hearts and to unite out of fear of driving people away from what is beneficial, just as the Prophet avoided building the Ka'bah on the foundations set by Ibraaheem (Abraham) because (the tribe of) Quraysh were new Muslims (i.e. they just came out of Jaahiliyyah – the Pre-Islamic Era of Ignorance) and he feared that if he did so, then that would repel them from Islam, and he considered that the benefit of being united took priority over the benefit of building the Ka’bah on the foundations set by Ibraaheem. Once, Ibn Mas‘ood prayed behind ‘Uthmaan, and the latter completed the prayer [during Hajj – i.e. praying four units of prayer instead of two], although Ibn Mas‘ood used to object to that. The people asked Ibn Mas‘ood why he finished the prayer behind him although he objected to him, and he replied, ‘Differing is evil.’ It is for this reason that the Imaams, such as Ahmad and others, stated this in regard to saying the Basmalah and praying the Witr with one Tashahhud, and other matters in which one leaves what is better to what is permissible but outweighed (in excellence or virtue) because of taking the unity of those led in prayer into account or in order to teach them the Sunnah, and the like.”
Therefore, these easy issues that are subject to Ijtihaad (personal reasoning) among the scholars should not be a cause of conflict and dissension.
Allah knows best.