Eh... I feel like I hear claims of both directions. The Chinese internet is full of people claiming that Taiwanese people can't read simplified Chinese or that PRC people can't read traditional Chinese.
FWIW, anecdotally every mainland Chinese person I've met has been able to read traditional characters. For some of them it is, however, more laborious. All of them have been able to read long tracts in traditional Chinese (think the length of a newspaper article or longer), although sometimes it takes obvious effort. This has not been true of some Taiwanese people I've met for simplified characters.
I'm mostly tempted to chalk this up to environmental factors rather than reasons intrinsic to the script. The mainland often gets a lot of Taiwanese cultural imports, while I don't think Taiwan gets as much cultural imports from the mainland. Furthermore there is a lot of stylistic usage of traditional characters in the mainland (posters, store signs, branding, calligraphy, artwork) and university-level Classical Chinese language classes (aimed at domestic students) are often taught exclusively with traditional characters. In comparison there is essentially no usage of simplified characters at all in Taiwan.
The two scripts essentially have a one-to-one correspondence with each other anyways so it's not really that hard to go between the two if you have full fluency in one.
I would argue that, due to merging different characters together, simplified Chinese is more ambiguous in meaning than traditional Chinese. So it's harder for someone more versed in traditional to read simplified, since there's a bit of guessing as to which "mapping" back to a traditional character should be taken. Whereas there's only one way to map a traditional character to a simplified character, so it's just memorization+recall if you learn simplified first.
I'd compare reading simplified Chinese characters after a traditional-Chinese education, to reading Japanese written purely in kana, and trying to figure out what kanji are meant. It's something that requires active use of your brain sometimes, where the opposite—translating kanji to kana—is a rote task.
As a note, although simplified merges far more characters than traditional, it also splits some characters that are merged in traditional. For example, 乾 in traditional is split into either 乾 (qian2 one of the hexagrams) or 干 (gan1 dry) in simplified.
Regardless, the number of simplified characters for which the merger of traditional characters happens is small, even more so compared to the number of Chinese characters you see on a day-to-day basis. On top of that, the vast majority of these mergers involve one character that in traditional Chinese is archaic and very rarely seen or are considered obscure variant characters of the same word in traditional Chinese. I can only think of maybe a dozen or so examples that show up in Chinese you're likely to read on a day-to-day basis. Even fewer if what you're reading doesn't have a lot to do with ancient China. That's why I say it's essentially a one-to-one correspondence.
I do hear your argument often from other Chinese speakers to support why reading traditional characters if you only know simplified characters is easier than reading simplified characters if you only know traditional characters so maybe there's something to it.
FWIW, anecdotally every mainland Chinese person I've met has been able to read traditional characters. For some of them it is, however, more laborious. All of them have been able to read long tracts in traditional Chinese (think the length of a newspaper article or longer), although sometimes it takes obvious effort. This has not been true of some Taiwanese people I've met for simplified characters.
I'm mostly tempted to chalk this up to environmental factors rather than reasons intrinsic to the script. The mainland often gets a lot of Taiwanese cultural imports, while I don't think Taiwan gets as much cultural imports from the mainland. Furthermore there is a lot of stylistic usage of traditional characters in the mainland (posters, store signs, branding, calligraphy, artwork) and university-level Classical Chinese language classes (aimed at domestic students) are often taught exclusively with traditional characters. In comparison there is essentially no usage of simplified characters at all in Taiwan.
The two scripts essentially have a one-to-one correspondence with each other anyways so it's not really that hard to go between the two if you have full fluency in one.