In general I'd agree that selling exp without gambling involved is better than selling exp via gambling, but not only is not selling exp at all even better, but your (OP's) posts also seem to contain quite many illogical points:
1. You seem to arbitrarily want Runescape to compete with other instant gratification games, even though there's a market for the opposite types of games (just look at OSRS for one) & Runescape was intended to fit that market, rather than the "if you don't want to play or don't have the time, just pay to skip most of the gameplay". As it is, RS3 doesn't stand a chance against other games in the instant gratification category, because its graphics are inconsistent and generally not up to today's standards, as well as the combat system suffering greatly from the 0.6s tick system and tile system. There's a reason why RS3 has steadily kept declining over the years, because it doesn't fit the slow pace market anymore and it's not good enough for the fast pace market.
2. Even though you try to shrug the game integrity thing as unimportant, reading along the lines, I'm getting the image that you think that as long as something isn't against the rules, it's not cheating, which is why it feels to me like you think buying exp isn't cheating. If I read that correctly, that's just plain sad: getting something prestigeous in the game without playing the game to get it, whether against the rules or not, is and always will be cheating. You might not get banned or otherwise punished for it, but in common sense, it is cheating.
3. How is the second option even a consideration from your part? You don't agree with the gambling aspect of TH, but if you removed exp from TH and kept whatever remains in there, TH would still be disgusting gambling in a video game played by children.
Overall, when a game is already monetized, like RS is with membership, MTX have no place in it. MTX belong to F2P games only, since they have to profit somehow.