I'd say this practice still remains in some form, but the pool of "strongest" types has expanded a little: Dragon, Psychic, Ghost, Dark, Steel, Fighting, and Fairy. Disregarding remakes, there hasn't been a single cover legendary without at least one of those types since Gen III. The full list of legendaries and mythicals without these types since Gen V is as follows:As admittedly from GF (case in point: Lugia), lot of the old legendaryes got the Dragon or Psychic (or both) types purely because they were perceived as the "strongest" types.
(A total of 36 legendaries and 13 mythicals were introduced in this period, counting the Galarian formes of the legendary birds, but not the Ultra Beasts)
- Tornadus
- Thundurus
- Landorus
- Volcanion
- Type: Null
- Silvally
- Zeraora
- Regieleki
- Glastrier
(out of a total of 28 legendaries and 9 mythicals)
- Articuno
- Zapdos
- Moltres
- Entei
- Raikou
- Suicune
- Ho-Oh
- Regirock
- Regice
- Groudon
- Kyogre
- Regigigas
- Manaphy
- Phione
- Shaymin
- Arceus
In addition, the types are found on all pseudo-legendaries, all secondary types of fully evolved starters from Gen V onward, all Ultra Beasts except Nihilego, Xurkitree, and Poipole, all fully evolved Alolan forms bar Golem, and all Galarian forms bar Darumaka and Darmanitan. We're at the point where not being part Dragon/Psychic/Ghost/Dark/Steel/Fighting/Fairy has become a bit of an exception for "strong" Pokémon.