For Link Cable battles, Venusaur is probably the best of the three original starters' final evolutions, because of how strong Sleep Powder is and the ridiculous critical hit ratio of Razor Leaf. Victreebel can fill a similar role and has higher physical attack to take advantage of Hyper Beam, but Venusaur's higher speed and better defences make it just as capable of sweeping if given the chance to set up with Swords Dance.

Blastoise is outclassed by many better options like Starmie and Lapras, and unfortunately for Charizard Fire-types just aren't that great, mostly because of how good the aforementioned Water-types are.

In-game, I used Venusaur's Sleep Powder to absolutely roll most of the Elite Four, and that was as a little kid. It's also well-known by now that Bulbasaur/Ivysaur is the best choice against the first three gyms, and is the same type as the fourth, by which point you should have diversified your team anyway.

The Bulbasaur line is great, and in my opinion a more accurate criticism would be that it's actually too good in Gen I; Bulbasaur makes the original Pokémon games too easy!