So all in all, this seems like having no real bite whatsoever, and is just a vague declaration of intent, which would, in practice be of no importance whatsoever compared to actual real world politics or military strategies of the individual countries.
The same is true about the language of the NATO treaty though.
So depending whether you want to see the empty or the full half of the glass, this is just as bad or just as good.
And as if this were not enough, perhaps to rub it to Trump (and perhaps even to the UK given Brexit), France and German made treaty in 2019 which has more or less the same clauses but with some stronger language. This analysis is worth quoting for the 3-way comparison:
The Aachen treaty can be triggered
in case of an “armed attack” (“agression armée”
in French, “bewaffneter Angriff” in German).
Likewise, Art. 5 NATO and Art. 42.7 TEU can
be triggered respectively by an “armed attack”
and an “armed aggression”, which are strictly
equivalent concepts from the legal point of view
as indicated by the explicit reference made in
both clauses to Article 51 of the UN Charter on
the right of individual or collective self-defence.
Indeed, the only distinction between Art. 5
NATO and Art. 42.7 TEU on the one side, and
the Aachen defence clause on the other, is that the
latter does not explicitly mention the UN Charter
(an absence with no real consequences, however).
The wording of the Aachen mutual defence
clause should rather attract our attention on
another point: the binding character of its
provisions. The Aachen clause states that
Germany and France “afford aid and assistance
to each other by all the means at their disposal”.
Those are significantly more muscular terms
than Art. 5 NATO, according to which each
party only has to take “such action as it deems
necessary”, which leaves a significant margin of
discretion in terms of the assistance effectively
provided. The terminology of the Aachen
defence clause is much closer to Art. 42.7 TEU,
which provides for “an obligation of aid and
assistance by all the means in [the Member
States’] power”. But there also is a relatively
important difference between Art. 42.7 TEU
and the Aachen defence clause. Although the
EU mutual defence clause creates a powerful
obligation of aid and assistance, a caveat is
immediately introduced: “This shall not
prejudice the specific character of the security
and defence policy of certain Member States”.
The possibility is thus created to modulate the
aid and assistance provided, even in case of a
successful activation of Art.42.7 TEU. The
Aachen Treaty does not contain any such caveat.
And I'm willing to bet that the CSTO treaty has equally flexible language, judging by how Russia recently interpreted it in the war between Armenia and Azerbaijan (of 2020), i.e. they were only willing to defend what Russia sees as Armenia proper. And actually even when the latter was attacked in 2021:
Pashinyan [...] made an official request for help to the CSTO in spring 2021, when Azeri troops moved to re-demarcate the border between the two countries and, according to Yerevan, sent up to 1,000 troops to take up positions on Armenian territory, resulting in deadly clashes.
The request for help was declined at a ministerial summit in Dushanbe. The decision to use force to protect a CSTO ally must be made unanimously by the heads of member states, and the annually rotating CSTO chair must first raise the issue. [...]
The Armenian public unsurprisingly viewed its allies’ attitude as nothing short of a betrayal. Of all its members, Armenia had always pinned the most hope on the CSTO, since the threat of war there is very real. Now polls show that just 7 percent of respondents would count on assistance from the CSTO.
On the other hand, I'm pretty sure Belarus can count on Russia to defend it from NATO, even though it's the exact same treaty involved.
Comparisons aside, 42.7 was invoked by France following the Paris attacks (by ISIS) in 2015, asking for both direct actions against ISIS and an increased participation in burden-sharing in France's other anti-terrorism missions, especially in the Sahel. The results were various votes in national parliaments of EU countries, with some countries like Netherlands or the UK agreeing to strike ISIS and others like Germany agreeing to increase military support for France elsewhere. On the other hand, e.g. Italy declined to participate against ISIS in Syria. It's hard to give a concise summary--the link has a table that spans many pages.
