I think that this discussion covers a lot of different things. First of all there are many in organisations that make statements on regarding things that they have no idea what they are talking about. By saying that Lets Encrypt does not sound legit falls into that category. (It’s like some don’t believe you can get anything for some financilal cost.)
The name Lets Encrypt originally defined the ethos of the target so was good. There may be a worthwhile discussion in the future for a name change but that is not now in my opinion. It’s not worth changing unless there is a lot of confusion or there are other enhancements that a change of name can reflect. Acceptability being one of them but with a stated over 50% share of the market that appears to be hard to prove.
That Twitter response happens a lot with other things and is because the answer was not defined properly. So instead of “Lets Encrypt” a statement such as “Use a Lets Encrypt certificate.” Not everyone knows about SSL/TLS means other than it is a certificate required for secure websites. They don’t know how it works, etc or the names behind them. Hence why we are the UK saw advertising to the general public by the likes of, if IRC, Symantec and GoDaddy did it indirectly by their Webhosting television campaign. There are many web developers who only know that they need a certificate and not a lot more.
I personally do not have a lot of faith in the higher value and priced certificates or the claimed insurance benefits. In most cases the Lets Encrypt certificate will suffice. However a bank, government, utility company, etc is likely to want everybody to have general respect for their security so will go for a paid certificate. So they may have used a Symantec one that is, in my opinion,virtually in the junk scenario these days and will take a lot of effort to recover. And though there are web hosters such as Rochen that work with Lets Encrypt, there are still those that see there income dwindling and do everything to dissuade or prevent the use of non paid certificates. I have shared hosting with Arvixe for testing purposes and they also want to be paid for certificates, but I put up with manually every three months authenticating and installing a certificate. However for production that is not sensible so you then have to use somebody that allows Let’s encrypt with automaic renewals or pay for one. And I started using ZeroSSL when it first came on-line and have continued to. The guy or guys behind that need a big slap on the back.