Not a pay driver quite, but you would have to put Jenson Button into that category. Much as I like him and am very pleased for him that he finally hung up his boots with a world title to his name he won courtesy of being in the right place at the right time. He had some ability certainly, especially in wet or drying conditions but he was never in the class of Hamilton, Alonso, Vettel, Raikonnen etc. Ross Brawn stole a lead on the rest of the field with car upgrades making his one and only season as team owner very much of a cake walk. A clearly superior car can make an average driver a world champion. Sadly, the best driver in the world has no chance in a poor car.
On the subject of winning in multiple teams, the only three drivers to have won five or more titles all did so in different teams. Schumacher with Benetton and Ferrari, Hamilton with McLaren and Mercedes and Fangio with no less than four teams (who can name them without having to google it I wonder?). I'll put you out of your misery ... Alfa Romeo, Maserati, Mercedes and Ferrari.
Schumacher's five titles for Ferrari came in a clearly superior car, but don't discount them because of that. The car was only so good because of his ability to work with the mechanics to make it so. When he moved to Ferrari they had not won a title for nearly twenty years, going back to the days of Jody Scheckter in the 70's. His two titles for Benetton came in a car which was not in the class of the Williams and McLarens of the day. The Ford engine in his '94 title winning car (Ford's last title winning engine) was way behind the competition.
It is impossible to compare drivers of different eras. The sport changes so rapidly and the demands on drivers likewise.
Firstly you have to manouver yourself into a competitive car. Take Alonso as an antithesis of that. He was (is) a superb driver but burnt a lot of bridges which on more than one occasion cost him drives at top teams. Everyone raised an eyebrow when Hamilton moved from McLaren to Mercedes, but it turned out he knew what he was doing.
A modern driver has more to think about than jumping into a car and driving fast. He has to be able to work with the mechanics to maximise the car. In that respect, in my opinion at least, Schumacher was peerless on that front.
Once you've got yourself in a competitive car and made sure it's the very best it can be you then need to produce in qualifying which is so important in the modern era when overtaking on track is so difficult. Nobody can match Hamilton in that respect. When the chips are down time after time he aces the perfect lap just when he needs it. Vettel on the other hand has made at least five errors in final qualifying this year which have cost him grid places.
And when you have your car at, or near the front of the grid you need to manage the race. Sadly, Grands Prix are no longer about pressing the loud pedal and going as fast as you can. Fuel restrictions, engine management and mickey mouse tyres are just a few of the things that team and driver have to manage during a race. For much of a modern race drivers will not be flat out but driving to "vector times", time set by the team to ensure that everything lasts as long as it needs to in order to produce the best race time. Again nobody comes close to Hamilton's ability to do that. He can produce lap after lap after lap within a few thousandths of a second of his target times. It might sound unimportant but that ability means he avoids having to turn down his engine mode late in races to eek out his fuel, or give him the ability to boost it a little when he needs to overtake. It means his engines last the required number of races without gird penalties for extra components.
This season for me has answered a lot of questions. It is highly unlikely that you will ever see Hamilton and Vettel race alongside each other in the same team. The Alonso / Hamilton experiment at McLaren (2007) proved the folly of two "alpha males" in the same team. It doesn't work. They fought each other all season and because of that both missed out on the title by 1 point to Raikonnen whose team mate (Massa) was ordered to defer to him in later races. So 2018 May well be the best comparison between the two. Statistically, the Ferrari has been the faster car in at least 11 of the 19 races to date, but with three races to go it is Hamilton in a Mercedes who is already holding the drivers title, and barring a miracle Mercedes will add the constructers title in Mexico this weekend.
Why? Because when the chips were down Hamilton took everything he could from every race. Mercedes even learned to play the team game, much to the dislike of both drivers. Vettel on the other hand has made mistake after mistake after mistake costing him serious points.
Is Hamilton one of the greatest. Easily. Is he the greatest ever, it is impossible to compare. Is he the greatest of the post Schumacher era? Easily. Head, shoulders and any other body part you care to mention above anyone else on the grid today.