grammar - Difference between してこのかた and して以来

These two grammar points seem to be synonymous. Apart from formality このかた being maybe an older expression, are there any significant differences in meaning between these two.

For example, is there any reason that

あの山の写真を見て以来、いつかは登ってみたいとずっと思い続けてきた。

could not be rewritten as

あの山の写真を見てこのかた、いつかは登ってみたいとずっと思い続けてきた

Likewise, is there any reason that

日本から帰国してこのかた、毎日日本のことを思い出している。

Could not be stated as

日本から帰国して以来、毎日日本のことを思い出している。

I took these examples from 新完全マスターN2.

Answer

このかた isn't felt older to me, but they do have a little difference in meaning.

Both ～して以来 and ～してこのかた can be translated "since X", but 以来 tend to focus on X, suggesting it is a notable, important turning point, or reference point to explain the story thereafter. In contrast, このかた puts focus on the period after X, that has significance, being long, full of memories, or whatever special, but X itself is usually incidental. In other words, 以来 actually means "Having begun from X, —" while このかた means "In all the time between X and now, —".

Your

あの山の写真を見てこのかた、いつかは登ってみたいとずっと思い続けてきた

thus sounds stiff to me, as this sentence apparently means you start to want to climb that mountain because you saw the picture. The second rewording is natural and almost synonymous.

Usage-wise, it should be noted that このかた is hardly used when telling objective frequency. Even if you said 就職してこのかた三回目, it would only be understood that you wanted to say "three times" is too rare, or too frequent, compared to such a long, or short, duration.

Grammatically, 以来 has a predicative meaning "be the first time since". このかた can never be used as predicate.

酒を飲んだのは、大学を卒業して以来だ。
= 酒を飲んだのは、大学を卒業して以来はじめてだ。
= 酒を飲んだのは、大学を卒業してこのかたはじめてだ。
× 酒を飲んだのは、大学を卒業してこのかただ。