Well, if Telegram had end-to-end encryption enabled by default, this wouldn't even be technically possible.
Seriously, disregarding trade-off between security and usability is exactly how we ended up with very secure, 20-digit passwords, containing every possible unicode symbol, updated every Monday, written on post-it notes hanging on the wall.
Pick a threat model and stick to it.
If you're seriously worried about communicating without trusting your phone, then you either need to find communication devices you do trust, or else look into verifiable TRNGs [0], dumb serial printers that can be directly attached to RNGs [1], and either manual encryption/decryption algorithms [2] or one-time pads.
WhatsApp doesn't have a native (or near native Qt app as Telegram does) on anything but phones. No tablets, no desktop OS. This is bad usability.
If I sign in to a new device on Telegram (and it can be nearly any device), I can instantly have my entire message history available. This is what they mean by chat history.
I no longer actively use Telegram, but only because no one else I know could be convinced to use it over Messenger. Messenger solves some of these problems but not all.
I can understand it'd be very annoying when you're affected -- eg having to work in an area with ethernet, but without wifi/3G, or when you need a fallback when the phone is out of battery. For the most part, it's a non-issue for me.
Signal uses the same basic protocol and doesn't require the phone to be online all the time.
Chances are the WhatsApp implementation chose a trade off that minimized confusion for less sophisticated users (within the constraints of maintaining confidentiality). That tends to be a good idea when you've got a billion users.
If I sign in to a new device on Telegram ..., I can instantly have my entire message history available
Including "secret chats"?
Telegram has a lot of users as well. It's a design choice for sure, but I disagree with it and it doesn't work for me personally. Their lack of support for anything but phones is my primary concern though - I could maybe stomach the requirement for my primary device to be online, but simply not making at least an iPad and preferably a macOS app is a no go for me.
> Including "secret chats"?
No, Telegram secret chats are device to device and can't be backed up or transferred. This is also why I rarely used them.
First off, as long as I have any device with chat history online — it is possible for my new device to inherit it as well. It's fine even if I have to confirm manually that session keys are equal or whatever.
Second, note that history can be stored on Telegram servers in encrypted form, I only need to have some secret key that is never sent to Telegram. This way "backing up the history" wouldn't be any different from "sending a message". And being responsible for taking care of my security keys is entirely reasonable.
Third, remember that primary Telegram credential is your phone number — something I abhor, but as long as this is true, I do need to have my phone to log-in on a new device anyway. By the way, I never tried to see if it actually works, but I would rather not being able to access my history after losing my device at all, rather than accepting that anyone who will get in possession of my phone number will be able to read all my chats. "My phone number" is not "me", for fuck's sake. (Yes, I know about 2-step auth, but we are talking about defaults here.)
And, honestly, I guess I would be fine with anything more or less usable, all I really have to know is that "normal people" do use WhatsApp and do find its usability ok. This means they would accept secure chats by default in Telegram as well. How long is it since you lost all your devices that can host Telegram at the same time, anyway? It is rarely the case that anyone's I know devices are all off at the same time, let alone lost.
Wire [1] already has both end-to-end encryption and cross device sync. It's not the only one to do that either.
It's not a tradeoff.
I only wish it had a better desktop client, the current one is a little laggy especially when scrolling up chat history.
Does Wire have a light-weight and solid desktop client yet?