The point of Signal having end-to-end encryption is to avoid trust. Telegram, on the other hand, relies on trust. Obviously that's going to attract more criticism.
On the other hand, while you are totally right about Telegram being quite a bit “trust us”; but they have better UX and are not at all hostile to third party clients and alternative implementations of their “secure” messaging protocol.
Which is also the subject of a lot of controversy of course, because (*puts on tinfoil hat*) it was originally handrolled and not US cryptographer approved.
(always get downvoted when I point out that Signal is doing weird stuff which only serves really to solidify my stance)